Now Smokin' didn't read your post quite right as from from 1:30 "in the morning" to 6:00 PM makes about 16 1/2 hrs.
Lots of people here have been finding it takes 2+ hrs per lb. But you have to remember that no two butts are the same. Each one is going to cook differently. And for some reason (maybe it's just me) it seems like the first smoke takes the longest. Anticipation...?

What works best for me is to start my smoke just before turning in for the evening with the temp set at about 185˚. I crank it up to 225˚ in the AM. Absolutely no need to mop. This is a very moist smoker!
Glad your first butt was a success even though you had to use alternative methods. At least you're thinking ahead!
Have fun & Good luck!

GHL - Go easy on him. He's new!!!