Days, maybe weeks. According to how much vegetation you contact, ground moistness, other variables as well, I suppose.
LT
I don't believe this to be true, LT.....but I'm no expert. I don't see how this would be possible if you go in clean....rubber boots.....etc... I think they can tell where you've stepped .....due to the disturbance of the vegetation....but I don't think we're leaving that much scent on the ground by just walking in.
Maybe I'll learn something in this thread.