There is plenty of info, I keep posting a generic answer repeatedly so do others.
Hellenic Seaways post their timetable and booking facilities around April for the Flyingcat 4. You get an earlier arrival time in Santorini (15:30) by using the Seajet Mykonos(10:00) to Paros and then the Bluestar ferry.
Welcome to the Greek forums! You can find a wealth of information on TA by using the search function. One of the most frequently asked questions is how to get from Mykonos to Santorini by ferry. Actually, the FlyingCat 4 timetablefor 2010 has just been published, much earlier than usual this year:
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