I've had my success mostly off of grunt calls. I usually do a tending grunt call. I start to call, well I started to call last night, to give you a time frame. I will continue now until I stop bow hunting. I didn't get any responses last night (wind might have had a big play in that as gusts were over 30 mph), however I have taken Good bucks off of it, and have had lots of responses prior to this date, as early as the 15th of October. A tending grunt is one which that you do 4-6 short bursts...when I say short, I mean short. Stagger the time between each. Try to make it sound as if you were running through the woods yourself. As you put a foot down, you are more likely to exhale. I usually do about 2-3 sequences within a minute or so, and then, I wait about 15 minutes or so. Also, keep in mind, the land I've hunted is big land, with small wood lots. So the deer usually "High tail it" from wood lot to wood lot, which can distort their hearing when I actually call. I have had this success in big woods in Northern WI as well. Where I took my biggest buck to date with a bow. I generally move the grunt call around(side to side, as well as behind me, up in the air, you name it...mostly where I have seen does come from earlier in the season), since the grunt call is a focused sound. It's not like a rattling bag, or a doe bleat that regardless of where you hold it, or point it, the sound is almost as similar if you didn't move it at all. Everything a hunter does is pretty much debatable, but don't be afraid to call. I would say 15-30 minutes, depending on your area you are hunting is a good rule of thumb.