Yep, I think the window is pretty small to do it effectively. I started watching how the bucks were acting starting on October 16th, and have been doing it for the last 11 years. The only reason is because this is the date that I had my first experience grunting a mature deer within range. I am still a rookie and learn a little more every year.
For me, October 16th through 28th are great times to call. I do the "sparring" for the first week, it has been moderately effective but mostly young clueless bucks come to investigate. I call them fly by's.
We just got a decoy a couple years ago and yesterday was the earliest I have tried it. A small 6 came in early, saw the decoy, at first he seemed spooked. 5 mins later he popped out above the decoy and was relaxed and it definitely peaked his interest. No signs of aggression or any of that, more like "hey there's a buddy, gonna say hey". Was gonna video the encounter but I think I stunk and thermals got me.
My best time for aggressive calling has been the first week if November. The days that I see bucks walking heavy footed, eyes straight forward, almost looking in a daze are when I have my best results. Have a few ideas why, but for whatever reason it works. I have never done it while a buck was on a doe, it seems like when I see more bucks and little to no chasing is the magical time. 2 years ago I rattled in 3 bucks. It was one of the coolest things I have ever seen. The timing was perfect and I watched 2 very big bucks fight.
I am still a little concerned with the decoy, I think it's just cause I don't know enough about using one and that scares the shit out of me. My luck isn't always the best and I am always thinking "worst case" scenario due to lack of knowledge....