Should I add wood every hour regardless of what the temp.? I'm not sure why I would do that if the temp is constant between 225-250.
Steve, watch the fire and add wood to keep a steady fire output. Plan ahead a bit so the new wood (or charcoal) has time to ignite before the temps drop. Many people run a second starter fire so the fuel they add is already lit; that's especially good if you're working with briquettes that have a stinky, smoky start-up. Lump burns cleaner.
Your OP is a bit sparse on the details, should we assume you are cooking with charcoal and adding wood chunks periodically?
Or are you cooking with wood splits only?
If you provide more detail it is easier to zero in and give you a more definitive answer.
If you are cooking with charcoal and adding wood for flavor then it is up to you when stop adding flavor wood.
I usually stop the smoking wood about half way through the cook. YMMV.