as one with a fluctuating schedule, I always try and do all the pre approval work before the time arrives - screening numbers etc that may take a week or so.

Im also upfront about it saying that my schedule is horrible and that I would rather make a last minute appointment pending availability than make something that I can't or don't keep.

It is my loss if i try and I can't get in and as long as I'm upfront about it there isn't much more i can do. When I do get in, I try and stay at least an hr however...