I do both solo and band work. As a solo in a 2 or 2 and a 1/2 hour show I normally do one hour before I break. I go longer, depending upon what's happening with the room and the crowd. If I am doing a four hour solo, I do two one hour sets with 15/20 minute breaks, and then play what's left in one shot.

With a band I have various experience. The current group I work with plans out the sets the way they want to present them, and plow on no matter what the clock says! I kinda like that. We do two long sets (one to one and a half hours) take a 20 minute break, and then a third set "cleans up" the rest of the evening.

I think the the 45 set you have been hearing is what people are used to, and works well. I think you need to find what you're comfortable with and stick with it.