Boil it for the hour it calls for. Adding some of the extract late in the boil will help to keep the beer closer to the color for the type of beer you are brewing. A Belgian Tripel's SRM is between 3.5 and 5.5. To put that into perspective, an American Lager, such as Coor's, is between 2 to 4 SRM.
Nevada Testsite Brewery
Bottled: Belgian Dubbel, American Pale Ale, Irish Red Ale (Yeast Fuel experiment), Doppel Bock
Up Next: Brown Ale