It depends on how bad I want the ADR!!! Also depends on why I'm changing it.
I've been making all of ours at 180 days out (insane) the last few trips, but if I want to change one and it's not available, I'd say probably once a week or so. This year, we're going the Thursday before Thanksgiving until the Saturday after, and I fully expect to be stuck with the ADRs I make at 180 days out.