Yeah it's hard to tell. Here's my thinking on them... If I see two "does" together then I always watch and see if there is a buck following behind closely. I won't shoot unless at least 10-15 minutes go by. This is ONLY during the rut of course. If no buck shows up, I start glassing even harder and trying to focus on their heads to see any dark spots where their buttons would be. If I never see a buck, and it's during the rut, my guess is they are twin button bucks and I'm going to let them walk. That happened to me Saturday night. Could've killed either one of them but decided against it b/c I didn't want to harvest a button. Now, if you see ONE "doe" by herself, I'd wait around 3-7minutes on a buck to show up and if I believe she's by herself and maybe already bred or not in estrous yet, then I'll take her.
That's just my philosophy......
...and on that day when my strength is failing, the end draws near and my times has come, still my soul will sing Your praise unending, ten thousand years and then forevermore!