Take a look at the rome2rio site. I took the train to and from Athens to Meteora. The site will show you how to do it from Delphi. I didn’t look for Olympia. If you get there early enough, you can easily do tours on your own. It’s a nice little town.
We rented a car there. The roads were fine.
I personally don’t like having any long drive on the day I fly out.

For what it’s worth, your Day 7 took us 5 days to do on our trip in April 2018. We didn’t make it to Meteora that trip, in our 2+ weeks. And our only island visit that trip was 2 days and nights on Hydra, closer to Napflio than many other islands. It seemed we could see Athens, Delphi, Galaxidi, the Peloponnese Peninsula, and Hydra, but northern Greece and any farther-flung islands would require another trip, or more.

In fact, we’re heading to Crete -just Crete- five weeks from now, for another 2+ week trip. In our limited experience, visiting Greece is much less costly than many other parts of Europe. But on 2-lane roads on the Peloponnese, with so many people cutting corners on curves, heading towards us in OUR lane, then moving back to their side in time, we drove even more defensively than usual, and it wasn’t like being on a 65 or 75 MPH Interstate highway in the USA. Long distances in Greece appear to mean a potential realllllllly loooooong day. If a rental car is involved, will you have at least more than one authorized driver, so that time behind the wheel is kept to a reasonable limit?

It is a busy itinerary, but very doable. I've done virtually the same trip, except for Santorini. We spent a more time in Athens, and a little more in Nafplio, but we had many things we wanted to see and do there.

I really enjoyed Mystras, so I hope you do visit. We took a long route through the mountains that day, and it was a long day. If you stay on the major highway to Olympia, it is a manageable day. Eating at Bacchus Tavern outside Olympia was a highlight.

The only concern would be that last day, needing to catch a flight. Remember you have to be at the airport a few hours early and have to drop off the rental. Any way to tack on day 12 to make it work? Or drive to Meteora on Day 9. Delphi does not take a full day, so you could see the site in the morning and drive in the afternoon.

The Greek countryside is beautiful and would be part of your experience.

Meteora is more than 200 miles from Athens. That is way, way beyond what I would consider a reasonable drive to the airport on departure day. If you encounter really bad traffic or have car problems, you'll be buying last-minute replacement tickets at the walk-up price ($$$$).

You cannot possibly see everything in Greece even if you have months at your disposal. Trying to do so can to lead to a rushed, hectic trip during which you spend a lot of time looking at your watch.

It pains me to spend this much time in a car in a foreign country but
we want to see everything.

You won't get to see everything. You'll spend your vacation days seeing lots of asphalt and boring highway scenery. There's no way of seeing all of Greece in nine days (notice I am not counting your arrival and departure days).

Of your total of eleven days of vacation, you've basically got four real sightseeing days only and seven travel days. To each his own, but for me, that would be a terrible ratio.

I don't agree with the opinion on Santorini expressed above (to each his own here too, of course); on the contrary, I think that Santorini is a great place to see especially for first-time Greece visitors. Yes, it is crowded and touristy and not "authentic", whatever that may be, but it's beautiful and spectacular nonetheless.

What doesn't make a lot of sense to me is spending basically three days of my valuable vacation time and getting only one full day of Santorini out of that. In your case I would have said: Stay on the mainland, that's more than enough for your nine days. But since you have already booked Santorini, I guess it's too late for that.

With those plans already fixed, I guess it's also too late for recommending that you put the Athens day at the end of your trip, which would give you more safety for your return flight. I agree with the others that I wouldn't want a long drive on the day that I have to catch my return flight. You may get caught up in bad traffic, or just imagine having any issues with the car... and you can wave good bye to your plane.

Also, you'll be pretty jetlagged on that first day and may not feel up to doing much sightseeing anyway, so it would have been a perfect day to move right on to Santorini and relax with a caldera view. Any chance of moving those Santorini dates still?

You haven't told us what time of year you will be going. Might be helpful to know for more advice.

Great comment by Anna. You arrive in Athens at 4. Instead of commuting to central Athens find a connecting flight to Santorini. You will need 2 hours for that. Getting over jet lag in Santorini is better than Athens. Spend your three nights in Santorini. The views are truly magnificent. Best way to Manage the crowds. Do not stay in Oia or Fira. Stay in Firoestafani its about a 15 minute walk into Fira but has the same Caldera views. For sunset viewing find a caldera view bar and make a reservation. Time it for sunset say 30 to 45 minutes before sunset. You get an unobstructed view, a seat and (expensive) drinks but it is a great experience.
https://www.flickr.com/photos/stanbr54/37622344154/in/album-72157689937827955/

Fly back to Athens and rent the car from the airport. Check out ACR Athens car rental. We have had very good experience with them.
Drive to Nafplio. On the way stop at Corinth to see the canal plus Ancient Corinth and Ancient Nemia. Nemia was a sister city to Olympia and had its own games plus stadium. You can still walk through the athletes tunnel and go to the starters line on the stadium floor.

We have driven to Olympia from Nafplio. It is a very long drive 5 hours and that's without stopping at the many ancient sites along the way. You might consider dropping Olympia and adding that time to Nafplio. It is also a very long drive Olympia to Delphi. Plan to arrive Delphi in the afternoon and visit the museum. The tourist buses will be gone by late afternoon and you can enjoy the amazing views down the mountain from Delphi village. Next morning get to the site early before crowds arrive. Tour buses will be arriving between 9 and 10 but by then you will be way up in the site and won't incur crowds for at least another hour. Now is the time to leave. Drive to Meteora. We stayed in Kastraki a village nestled at the foot of the mountains. I see you are thinking about a sunset tour. We simply drove up to the mountains near sunset and were able to scout out all of the Monastaries and took photos of the sunset. Next day there were at least a hundred tour buses and the whole place was crowded. Get up there early.
Now drive to Athens and spend your time there. You will be fully acclimatized to Greece and that plan will give you time to enjoy Central Athens and you will be in Athens with several different modes of transportation to the airport for your return flight.
Delphi and Meteora https://www.flickr.com/photos/stanbr54/albums/72157698930270992
Nafplio and Peloponnese http://www.flickr.com/photos/stanbr54/sets/72157632094108982/

We spent three days doing your day 7. Olympia was a highlight for us and many people told us to skip it. Glad we went there.

I'd go through each location, and identify what you want to do. There are a lot of things in Athens: Acropolis (#1 must see), National Archeology Museum (Must see), and about 6 other things. I'd do 2 days in Athens. Eliminate Santorini, put the time in Athens.

Have you cosidered Mycanae? Really key archeology site.

How many miles is this?

Eliminate Santorini

Too late...

so far Athens and Santorini are booked

Meteora is awesome, but I spent 3 nights in Trikala (about 20 km away) when I visited that part of Greece. Unless you can tack on a few more days to the end of your trip, I don't think you do it justice and should save it for a future trip. Claim back that time for the Peloponnese or Athens, and have a less stressful end to the trip.

Also OP appears to be a 1HW.

What's a 1HW?

What's a 1HW?

My guess is 'one hit wonder'

I would not want to be a 5 hr drive from airport on departure day..

If the 4PM flight goes to a Schengen zone destination, OP needs to be in airport ( after gas fill of rental car and turn in), by 2PM.

Any other destination necessitates a 1PM airport appearance.

Day 11 plan is a disaster waiting to happen

Oh, thanks. I had noticed that the OP has never shown up since that initial post.

I guess it is annoying to book first and then ask... and end up being told that those plans are far from ideal. You are right of course about the 1 p.m. airport appearance if he/she needs to get back to Philadelphia.

Thanks all.
I had a feeling it was too ambitious and just wanted to confirm with people who have been there.
Will dial it back and come up with a better plan for the second half of the trip.

1HW

:)

Hi Jake, good to see you back! (You're a 2HW now, I guess! :-) )

Let us know how your changed plans look if you like. Are your Santorini dates all fixed, or can you still rearrange that?

Jake - I'm glad you seem to have a good sense of humor or easygoing personality. Some of the posts in this thread have been very odd and even downright rude. I'm sorry for that.

As I noted earlier, your itinerary is a little aggressive, but the driving trip you have is not. Neither Olympia nor Delphi are towns I would recommend lingering in. The ancient sites/museums are fantastic, but the towns are good for an overnight accommodation. The drives are quite scenic. I've done that almost exact itinerary and really enjoyed it. I still recommend, as did many others, that you look at that last day.

Meteora was indeed the coolest thing we experienced in our 2-week road trip around mainland Greece.

Second coolest was seeing the Acropolis lit up at night from the open-air rooftop bar of our hotel.

Enjoy your trip!