hi bride,
sorry, couldn't check the forums earlier.
the best time to visit the greek islands is in late spring or in autumn, when there r few crowds n yet, most of the tourist infrastructure is still opened.
if u want to party, winter is the wrong time to be in many of the greek islands. when we were in santorini, the car rental companies told us that the number of winter tourists is only abt 10% of the number in summer! santorini is really a tourist island. many of the smaller tourist towns in santorini r closed totally. a few pubs in oia r open (we could hear the pounding music starting from sunset), but honestly, there r so few tourists, there really isn't much partying to be done.
as a result of the small number of tourists, i can assure u that there will be plenty of vacancies in all the hotels etc. there's really no need to plan ahead.
the ministry of culture has all opening hours posted online at
http://www.culture.gr/2/21/toc/index.html. i'm not sure exactly how much time u hv or what u want to visit. for myself, it was after consulting this list that i felt confident enough to go ahead with the trip. since u still hv time to plan, shortlist the sights n check if they r open in winter b4 making up ur mind.
a summary of my experiences:
1) santorini: the beaches r still accessible n they will be deserted. however, the akrotiri musuem was not opened in feb when i visited. i read later that the musuem is closed for restorations, not sure if this is a winter thing or a multi-year restoration. the boat ride to the volcanic hot springs was not operating. the scenery was gorgeous still. overall, i will say it's pretty ok for a 2-day stay but i probably wouldn't stay longer.
2) we didn't visit mykonos, but i checked b4 i left that delos (the birth place of apollo) is definitely opened until 3pm everyday.
3) in crete, knossos palace, heraklion musuem, fortezza fort, musuem of rethymno, r opened almost everyday (if they close, it's usually on mon). however, operating hours r usually shorter, usually until 5pm, but sights in rethymno close at 3pm. the musuem of rethymno is not really worth the time lah. the thing that really sticks in my mind was the coin collection.
one thing to note when planning ur f&e. i checked with my husband, who visited mykonos some years back on new year's eve. new year (jan 1) n christmas (dec 25-26) r holidays in greece. my husband said mykonos shuts down during those holidays. projecting my experiences in vienna on christmas, u might want to check the opening hours in italy. hardly anything was opened in vienna on christmas. so remember to take these into acct when planning.