Need Help with driving Itinerary Meteora, Delphi, Olympia, Nafplio- Monemvsia-Peloponnese.

Yes, Olympia is worth it!!! Goosebumps stuff. Museum there is excellent.
Delphi- Yes you could “do” it in 3-5 hours. But the setting is incredible, overlooking olive groves down to the sea. Stay overnight and book a room with a view to the water beyond.
Napflio-way too far for a day trip to Monemvasia. You can day trip to Mystras, a Byzantine town that our Greek friends told us we HAD to visit. We were so glad we did. A change of historic periods.
Two nights is not enough for Napflio. You really need to add to add more time for this portion of your trip.
Driving times may be longer than expected due to winding mountain roads. In Greece you are never far from mountains or the sea.

I was planning on going to Meteora and northern Greece, but the pandemic squashed that. I intended to have at least two nights. Based on what I have read about Delphi, I think a night there would be nice.
I did not make it to Olympia, but not terribly far (less than two hours) from Olympia is Messene. I highly recommend Messene, it was an amazingly intact site--you won't need much imagination!
I also did not make it to Monemvasia, but I think you might want to leave it off based on your feeling about drives.
I heartily agree with Suki about Mystras!
Near Nafplio, we visited Mycenae and Epidaurus. We also enjoyed Nemea, which is sport-focused like Olympia. It is very small, but there are some very interesting things there, so you might consider making that your replacement if Olympia does not make the cut. It is close to the main highway back to Athens and it is a fairly quick stop. I think you might want more than two nights in Nafplio.
You might consider saving Meteora for a future trip if you need more time in the south. There are some not as dramatic but evocative in a similar way monasteries (and great hiking) in the Peloponnese near Stemnitsana. We went there after Messene, but it was a heck of a drive so maybe not!

We decided that a day tour from Athens to Delphi suited our style and time constraints well given the distance and the roads. We did not go to Meteora, but if we had added that we would have gotten a car and driven there, stayed the night in that area and driven back to Athens stopping in Delphi on the way perhaps overnight as you suggest, although that would not have been necessary. (the road not taken).

From Delphi I would recommend driving directly to Napflio to catch your breath and do Mycenae and Epidavros the next day. Then see how you feel about Greek driving conditions. We didn't mind, but used to live on several long two lane roads. If you choose not to go to Olympia and Monemvasi because of the driving you can drive to Ermolu easily from Napflio and catch the ferry to Hydra just off the coast. Ferry back to Ermolu and drive back to Athens, or if you can get other transport to Ermolu from Napflio you can take a ferry from Hydra directly back to Athens.

Have fun.

They are all worthwhile. It is more a question of what you have time to see. I would have fewer stops and more time in them.

We did 4 nights in Nafplio and enjoyed it by it was very hot and we spent every afternoon at a (different) beach. I would say 3 nights (but not 2) would be sufficient for most people.

Southern Peloponnese is not a day trip from Nafplio.

We did not go to Olympia as it was just too far. We did go to Nemea which was where games were held also and enjoyed it very much.

Ideally, I think you want 2 nights for Meteora and 1 night for Delphi. If you put Athens at end you could have an extra night.

2 nights Meteora
1 night Delphi
3 nights Nafplio
3 nights Athens

If you really want to see more of the Peloponnese, I would skip Meteora.

I don't think you can do all of this well.

We did a similar driving trip in this order - how long you stay in each place depends on how much time you have total for your trip. I've forgotten the driving distances between each city but use Google Maps or Rome2Rio to map out distances.

1. Athens (3 nights is good - we picked up our rental at the airport and headed out from there)

2. Nafplio (nice for a longer stay)

3. Monemvasia (1 night)

4. Kardymeli (a nice place to relax)

5. Olympia (one night here is good - I think it's worth it but if you're unsure, you could delete it!)

6. Galaxidi (as a base to visit Delphi or just as a stop by - not necessary to spend the night)

7. Meteora/Kalabaka

8. Thessaloniki (or back to Athens)

Adding that I agree with BethFL and valdelphia- Nemea is a good alternate to visiting Olympia - they have a nice museum related to the Olympic games and it's an easy day trip from Nafplio. For 9 nights, BethFL has a pretty good plan.

You have received good information. I too think the 5 hour drive to Olympia takes too much time. Sometimes when you do less you have a richer experience in the places you get to.
Perhaps a few images of these places may help you prioritize you destinations.
Nafplio https://www.flickr.com/photos/stanbr54/albums/72157632094108982
Delphi and Meteora https://www.flickr.com/photos/stanbr54/albums/72157698930270992

If you do visit Meteora consider staying at Kastraki. Its a small village nestled at the foot of the mountains.

when we stayed there our hotel had a view of three Monasteries. It is way closer than Kalambeka which means you get to the Monasteries before the bus crowds arrive.

No one has mentioned the area around Corinth except for Nemia. You can spend a full day in Corinth seeing the canal, Ancient Corinth the huge fortress at Acrocorinth as well as Nemia.
Corinth Area. https://www.flickr.com/photos/stanbr54/albums/72157711755443483

Peloponnese, Mani and Monemvassia. https://www.flickr.com/photos/stanbr54/albums/72157711323535897

We opted for an overnight in Delphi mainly in order to be at the historical sites before the tour buses arrived from Athens. It was a plan that worked well for us. IMO two nights in Nafplio are not enough; three would be the bare minimum. We used it as a base for day trips to Mycenae, Epidaurus and Ancient Nemea (which we chose in place of Olympia). Palivou Estate winery is very close to Nemea and our wine tasting there was very enjoyable. Have a great trip!

We did the following a few years ago (before heading for the islands) and found it perfect. Olympia was definitely worth it for us, but we are sports fans so it was a thrill to visit the site where the Olympic Games were originally held and where the flame is lit every four years. We broke the trip up by staying in a great mountain town and doing a short hike to hidden monasteries near there. The drive to Meteora from Delphi was long and we asked ourselves during the trip if it was worth it but were so glad we did it. We understand you can also take the train there from Athens, if they aren’t on strike (which they were when we were there):
Athens – 3 nights
Nafplio – 2 nights
Dimitsana – 1 night
Olympia – 1 night
Delphi – 2 nights
Meteora – 2 nights
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