I like to "milk" but not worry to make it last awhile.
What I do is ride waves, jump etc. real hard for ten minutes, then relax while going back upwind a ways and do "a third" of the same spot again. So, I could easily make it last 2.5 hours.

But, 1.5 hours easy for the average approach (of just slowly going downwind and never backtracking) or if you wanted to surf everything in sight and always go downwind and jump and go insane, 50 minutes. You could always start more north and stretch it that way, too.

Roberto and I rode from Sand Key to the Undertow 2 years ago.
I took my approach (bad idea) and after 3 hours we stopped short pretty tired (overpowered on C-kites and the edging upwind killed us... dumb).

That's a huge advantage of the trolley is that it doesn't matter where you stop. The trolley doesn't care what your original plan was. A girlfriend does, should you not ever get there and she is just waiting. Stuff breaks, and sometimes you have to stop short.