If a trap site hasn't been visited, how often should it be rescented and baited?

I see you have many questions young Padawan. Let me direct you to the jedi masters of trapping:

http://www.trapperman.com

Go to the forums there.

All depends on what you are trapping. If coons, mink, beaver, water sets I usually freshen every 2 days. Canines I do every 7-10 days. I stay completely away from the K-9 sets if there isn't anything in them. The others I'll walk down check for tracks etc.

Lots of variables to deal with here: rain, snow, temperatures, targeted animal, etc.
I refreshed my dirtholes about every five days if the weather was cooperative (no rain or snow). I refreshed them after each good snow and rain event. If you are using dirtholes the rain may wash dirt into the hole and cover up and dilute the scent you are using. One trick I used was to scratch away the snow from a set as a visual attractor. The animals could see the fresh dirt on top of the snow really well!

I dont claim to be an expert on this subject. But if that set is on location ,It should have a hit within the first few nights. If not, the trap would be better off in another location. I cant say that I always abide by this. because the coyotes in my area sometimes only come through certain areas once every five or so days. If my coon or fox sets dont produce results fast my time would be better spent in a different location.