If it was me I would choose between the two ancient sites, Delphi or Olympia. To see them all would be a minimum of 15 hours of driving whereas omitting Olympia would trim five hours off of that. Omitting Delphi would trim about 1.5 hours off of that. The two ancient sites are somewhat redundant and Delphi has by far the better views while also being close to several other terrific sites nearby (town of Arachova, monastery of Hosios Loukas, port / beach town of Galaxidi).
Stay at least one night in Kastraki, tiny village at the foot of the Meteora monasteries.
Personally, if it were me, I would drive to Hosios Loukas from Athens and visit the monastery, stop in the delightful town of Arachova for lunch and a stroll, and then arrive in Delphi in time for an as-late-as-possible tour of the ancient site (perfectly awesome idea to book a local guide for a tour here). I think they close at 8pm, so we usually show up around 6:15. Place is pretty deserted by that point in the day. Spend the night in Delphi.
Next morning visit the archaeological museum early to beat the tour buses and then drive to Meteora. Stop at Stone Bridge and Waterfall at Palaiokarya and Pyli Stone Bridge for a manageable detour (adds about 1.2 hours). Arrive Meteora in time to visit at least the one monastery that will be closed the following day (there will be one for each day that will be closed). Visit a second if time permits.
Stay the night in Kastraki and drive back up to one of the lookouts for spectacular sunset photography (around 8pm is perfect in summer) after dinner at one of the tavernas. Or, save dinner for after the sunset drive.
Next day visit the rest of the monasteries. I always try to get to Gran Meteoron as early as I can get there to beat the tour buses. There is always a huge line of people coming in when I am leaving and it can be hot in the summer.
On the way back to Athens you could stop at Trikala if you have time, but it's gonna be a four-hour drive getting back to Athens.
Pro Tip: Arrange this to coincide with your departing flight and you can drop the car right there next to the terminal and be on your merry way.