Seven-hour layover in Athens

Aegean Airlines keeps screwing with their schedule, so my perfect
itinerary with a short layover on my way back from Crete has turned
into a 7-hour layover (approx. 8 am - 3 pm). I've been to Athens
before and seen the Acropolis, the Plaka, Tomb of the Unknown Soldier,
and other sites in that central area. However, the National
Archeological Museum was closed, so I didn't get to see it.

Any suggestions on how I should spend my layover? I don't care to
return to the Plaka area, so I'm thinking maybe the National
Archeological Museum or the Museum of Cycladic Art. Other suggestions
are welcome too. In fact, I don't even care if I actually to into
Athens if there are other places within an easy trip from the airport
to visit. Thanks.