I have had them answer grunts year round, they are a very curious animal, so they tend to investagate the source of the grunt. Close to, or during, even just after the rut is the best time for your scents, grunting tigether, but I would aslo suggest some lite rattling too.
There can be too much of a good thing with antler rattling.
I like to hit the horns together for a good 30- to 40-second rattling sequence and then hang them up and resist the urge to hit them again.
This works to the hunter's advantage, because if a buck has heard it, he may have been 300 or 400 yards away and he comes in and he's not exactly sure where it came from.
When finally is time to rattle again throw a slight change-up into the routine.
The second time, don't rattle as loud...