How long to boil a scotch ale?

I'm going to be brewing a scotch ale pretty soon and I was wondering how long to boil the wort to caramelize it. Here's my recipe:

20 lbs pale 2-row
10 oz. crystal 120
8 oz. smoked malt
4 oz. roasted barely

1 oz williamette 60 mins
.5 oz williamette 30 mins

I plan on mashing pretty high so I can finish around 1.040. I'm not using a whole lot of specialty malt, I would like to get my sweetness from caramelizing in the boil, but I was just curious as to how long I should boil for that to occur. I usually boil most of my brews for about 2 hours, and was just curious if that would be enough or should I push it to 3 hours or even more.

You can either boil it longer or just take the first runnings off in another pot and boil it seperately, maybe to a thick syrup.

But then I typically do a traditional scotch ale with only pale malt and roasted barley, I think your's will turn out nice and malty if you just boil it longer, depends on your "boil".

You using one of the McEwans yeasts? or?

That should be fine, but I'd split off about 1 gallon and boil that down at least halfway while the rest is boiling to get some heavy kettle caramelization.

I'm going to be using safale us-05, homebrew shop around here doesn't have much in the way of yeast. Probably going to ferment around 55 degrees.