Timing of sights to see in Athens

The only advice I will give is get to the Acropolis first thing and be there just as it opens. This will help you beat the crowds.

We did this and it was easy to get in. By the time we left a couple of hours later, the lines were very long. And that was in late April of the that year.

From there it's an easy walk to the Acropolis Museum and the Agora.

The Acropolis, the Acropolis Museum and the Agora are all in the same general vicinity so you could plan on visiting them on the same day. The Acropolis is best seen either right at opening time or later in the afternoon when it is less crowded. When you are there it will be open until 7.30 pm. Personally I find the morning is cooler, important at a site with little to no shade and Athens is notoriously hot. The Acropolis Museum is just across the street from the Acropolis so I’d go there during the heat of the day and enjoy its air conditioning. There is a nice cafe for lunch. I think leave the Agora for the next day, lots to see there, including the Stoa of Attlos, the Hephaisteion Temple all in a nice park like setting.

The NAM is open til 8 pm in May so you might want to consider going there during the afternoon you arrive in Athens. It is a bit out of the way of the other sites. It is a stunning museum, a true treasure house. The bronze statues, wow! the Minoan and Mycenean gold work - oh my! I spent the best part of a day there and only scratched the surface.

Some practical information to complete the previous ones:

If you want to book in advance, tickets for May will only be available from April 1st, when the rates change to the summer rate.
Regarding the Acropolis and only the Acropolis, it is mandatory to book a time and a date. You will have to be at the access gate within 15 minutes before your reservation time.

For the Acropolis, Agoras, and the NAM, tickets can be purchased on the official website here:

https://hhticket.gr/tap_b2c_new/english/tap.exe?PM=P1P&region=000000007

The Acropolis Museum is under private management. The official website is this one:

https://www.theacropolismuseum.gr/en/

The NAM is the only place a little bit away from the other sites you want to see.
From Plaka / Syntagma square, by taxi it's 10/15 minutes and a few Euros. You can also take a trolleybus line 2 or 4 or 11 from Syntagma square and get off at the Polytechneio bus stop.

About the Nat. Arch. Museum, I will only add this comment to Jo Lui's excellent help (she is a Treasure!) -- this is a Huge World-Renowned Museum ... and ideally would have tours onsite that you could book, or at least volunteer docents. However, in my various visits, nada (hope this has changed). However Rick to the Rescue! On this website (click upper-left of this page "Watch, Read, Listen") he has FREE downloadable audio guides - to the Acropolis, the Agora, AND the Nat. Arch Museum. The last one is more on the llines of the "10 top treasures" -- and can steer you there. It saves you getting lost in long corridors of Pots pots pots...and you can see a lot in a couple of hours.

The other 2 audio guides are also v useful, because IF you use them right (and it always helps to read some stuff too!), you are not tied to the timetables of group tours. While some are excellent, they typically start around 9 am and that is when Acropolis is PACKED. With your self-guide, you can get there early, OR at 5 pm, when crowds mainy have left. IMportant: listen to audio guides beforehand, so you'll be familiar, & won't lose your place.

It’s been awhile since we were there but I seem to recall the entrance to the Acropolis is on the west side, the Agora is northwest, and the Acropolis museum is on the southeast. It was very easy to walk north to the Agora after we finished with the Acropolis. I think we visited the Acropolis museum the next day. We didn’t get to the NAM. Good luck with the trip!

Thank you all very much