If you think you can work something into a hunt then shoot it. I don't think there is a set time to gather b-roll. It kindof depends on how you want the final product to look. I for one don't add anything into my footage that I didn't get at the time of the hunt. Rarely if ever will you see any staged scenes in my footage. I shoot these incase I sell footage or loan it to someone else, but my productions usually do not use it. Because of this, I don't film alot of b-roll outside the course of hunting, scouting, or hunt preperation.