We did exactly the same as Frederick when we visited in 2007 - berthed the boat back onto Ios town quay and got the ferry. We stayed over for a night in a small hotel on Santorini plus hired a small car - others berthed alongside our boat kept an eye on her for us. If you've tight budget the slow ferrydeck passenger rate was around 1/3 the cost of a fast boat ticket.
Cheers
JOHN
I have been to Santorini 3 times, so for me 4 or 5 hours weren enough. If you come for the first time to Santorini it is a good idea to stay a night in a hotel. Spend 2/3th of the time in Oia en 1/3th in Thira. And visit Thira first, as Oia is much bigger and even more attractive. Thaou will also have the time to visit the excavations. Fr.