dont know since after Keith, but in august i think it was 10 pm, and later on wednesdays and saturday nites, like midnite or 1am. they alternate every-other hour, n-s. there was a posting of times outside rendezvous restaraunt.
I believe that's an old, pre-Keith schedule. The new schedule is much more limited. Keep in mind that there are two different animals-- the ferry (which is basically scheduled water taxi service) and on-demand water taxis.