I generally go for an hour to an hour and a half early.
I could see more if it's a nice place with a dinner crowd that needs to not be disturbed.
The thing is, the more of my time they want to get, the more of my time they need to pay for.
You may not have considered this, but you are enabling the bar owner.
Once he gets a free band, it will make him expect that.
Anyone making their living by playing in your area will not be happy.
At some point, you may find yourself needing to find spot in a different band.
That band may remember you as one of the guys that did the free gig that
that lowered the average pay in your area.
That said, if you agreed to it, do it.
I would suggest trying to see if the bar owner could do something to make it worth your time.
For instance, I used to do a recurring gig in a place that was primarily a catfish resturant before 9PM.
We'd set up 1 1/2 - 2 hours early and enjoy a great free meal until 15 - 20 minutes before show time.
Yes, we were getting paid, but the food made it worth while to be there early.
Can you get food, top shelf booze, a great view from the back door, a firm promise of money next time or
SOMETHING
to make it worth your time?