First let me say I respect the endurance and customer service!
If it's gone that long with no finish it means either 1) he can't finish - lotta reasons for this or 2) he can but doesn't want to and is stringing the time. I usually book 4 hour appointments, I go 3-5 times. Every once in a while I have difficulty with the last one. Sometimes I just say this feels awesome but it's not going to happen and we just call it, other times I try a few things that have worked before.
If he's honestly struggling but you think he can finish then the best suggestions I have are:
1) Stop trying, back all the way off (all the way to limp) let him totally reset, then try again. Guys can get a mental block, and their mind can focus on what's not working, which of course makes the problem so much worse. Backing off especially if the woman makes it "no big deal" works much better than just continuing what isn't working. After a reset I can usually finish in 10 minutes. If I can't in 10 it's not going to happen.
2) Try washing your hands in cold water, the temperature differential can bring more sensitivity.
3) Not sure if you use lube or not, but sometimes it's a help (feels nice) and sometimes it actually makes it more difficult (no friction), so you might try the opposite if whats happening isn't working.
4) How warm is the room? I've noticed that if my body temperature rises it takes me longer.
Hope this helps