Planning a trip in May which includes island hopping from Santorini to Folegandros then to Milos. The SeaJet schedules seem to be very limited as I check their site....do they typically add more ferries closer to that time of the year or should I book now. Friends of ours were there last year and took midday ferries between the islands...now the schedule only shows 7 or 8pm. I’ve checked ferryhopper as well as the Sea Jet site.
It's most likely that it's still too early for the full May schedules to be ready for publication. Last May there were indeed mid-day departures from Santorini to Folegandros and from Folegandros to Milos, but they weren't available every day, so keep checking for updates.
You can also check for those updates here: www.gtp.gr
You will not have to book in advance ANY ferries in may, they will be half-full except maybe friday afternoon leaving from Piraeus for a 3-day weekend. Look at gtp.gr -- often they will put on ferries with the notation "not yet approved". There are almost always a couple of ferries per day between the islands you name. The TOUGH ones in West Cyclades are Sifnos-Serifos.