I have a couple of "off-the clock" guys actually. For whatever reason, I have similar interests with a lot of these guys and end up taking them to concerts, plays, etc. I always pay for the activity but there is of course no "hourly" rate for the time we are spending together at those activities.
I always kind of think of it as I'm willing to spend money for a friend's ticket to a concert (or whatever) because I want to share that experience of something we both enjoy.
But of course any time we're in the bedroom, we're back on the clock and I pay the agreed-upon rates. In many cases (though actually not always) this is before or after the activity. I feel like it's worth it for them to enjoy something they would like to do anyway for free and then often still get some money after.
My only advice is to make sure it is something they really enjoy. I once took a friend who enjoyed theater to kind of a cerebral play and could tell he was bored. He loves theater but more razzle-dazzle musicals than Tom Stoppard.
