Previously I mentioned the new opening hours for the Acropolis. The New Acropolis Museum will also be switching to its summer hours.
One think I really like, is that unlike many places in mainland Europe, the museums are open on Mondays, albeit for shorter hours than normal.
Kathimerini (English Edition) 
Thursday April 3, 2014
Leading Greek museums and sites extend visiting hours for new tourist season
A number of the country’s archaeological sites and museums inaugurated extended visiting hours on Tuesday in view of the upcoming tourist season.
The Acropolis and the National Archaeological Museum in Athens, Crete’s Knossos, Santorini’s Akrotiri and the sites of Ancient Olympia and Delphi in the Peloponnese were among a group of 33 museums and sites set to operate on the new spring-summer schedule – daily from 8 a.m. to 8 p.m. – through the end of October.
The move marks the implementation of a national pilot program, while the selection of the 33 sites and museums was based on the number of visitors they attract. More are expected to join the program at a later date.
The Acropolis Museum in Athens has also modified its schedule ahead of the summer season and will now open on Mondays from 8 a.m. to 4 p.m., Tuesdays, Wednesdays, Thursdays and Saturdays from 8 a.m. to 8 p.m. and Fridays from 8 a.m. to 10 p.m.