can we visit delphi in a day?

Patricia Are you planning to fly to Delphi ? because ferry will be too long. That can be a tiring trip for a day. There are other nearby islands near Santorini that are around 2 hour or less by ferry for a quick trip such as Naxos, Mykonos and Ios. That can be an alternative for you.

Rjean, I think you have mistaken DELOS (the island off Mykonos) for DELPHI -- the sacred site high in the mountains. Patricia, to give best advice, we need fuller information. Without the "big picture" we're just operating off guesswork. When I see an inquiry like this, I immediately have questions:
• WHEN is your trip (june is a lot different from August or November_
• How many days has your trip been at that point? Just Athens-Santorini... or 2 wks island-hopping, or a guided tour?
• Are you "locked in" to an Athens stay with a nonrefundable Hotel & tour-signup, before your Island-going? If not, I would suggest doing a Delphi overnight as part of that "Athens Time"... and when u arrive back on that Friday, finish up with a final Athens day.
• When you say arrive Friday 1 am, is it by Plane, or from long Blue Star ferry trip?
• If Friday-Sat Looks like Delphi time, how would you want to get there?? You can't start driving at 2 in the morning, on an unknown road into the mountains. You can get a very reliable KTEL intercity Bus and snooze all the way I've taken these busses & they are modern, airconditioned, upholstered reserved seats, perfectly fine even for Americans that sniff at busses ... but the first bus out of terminal is 7:30 am -- and what do you do for the 6 hours in between?? And Tour busses start even later (& take longer)
• Are you a go-getter 30-something couple, in which case, you can go clubbing.... or a retiree couple who likes a good nap?

see what I mean? All the above affects advice.
... I've been to Delphi overnight, & it's MUCH better than trying to cram it into 9 am - 7 pm -- but can't help without relevant facts. please do share more!

Thank you for the responses and sorry for not providing more information...
We will be at the end of our trip.
We are traveling on our own, no commitment at the end of a week.
We return from Santorini on Friday, Sept 27 at 1 am.(flying back to Athens)
We leave Saturday to go back home to Philadelphia at 5:35 pm from Athens and i wondered if there might be any possibility of squeezing this in. :-)
I have not made our room reservations because I had this plan in the back of my mind. I know it would be a lot but I probably won't visit Greece again in my lifetime and there doesn't seem to be much to do around the airport for a day and 1/2, which was my original idea.
I like the idea of a 7:30 bus departure, but yes, we will have to do something else for the 6 hours. and no, I do not want to start driving in the middle of the night. We are two female colleagues who love to travel. I am the one who likes to fit everything in I possibly can, in case I never return. My friend, needs to be coaxed into it but usually agrees.

Let me know if you need any additional details....Thank you so much for your help.

Thanks for the pertinent details... and thanks To Kpesma1 for the private tour option! ... I clicked on it an it's €77 per person, but not bad at all, if true!! (A D-I-Y would cost about €35-40 each for KTEL bus/tax ... and no guide & no hotel pick-up). I would check this option immediately. ... and see if the Hotel pick-up is only for central Athens, or if they'd pick up out near the airport. If it's the latter, you might ( If u r well-fixed financially) go right across the street from airport building to Sofitel for a €200 room & sleep for 7 hours; if less affluent, free shuttle (fixed in advance) to Holiday Inn Attika about €125 or so.

You do not even have to stay overnight...

NOTE: I would carefully check on the credentials of that private tour -- since praising it, I have found that the poster has been ejected from 2 other Greece forums for "spamming" -- that is, posting on unrelated threads just to promote tour services. So one should be extra sure that the services are as advertised.

Thank you. The prices were too high for the private tour anyway.