Monkmonk, I often find my self in the same predicament of only having a short window of opportunity to pull off scheduling an appointment.
What has worked best for me is adding the ladies I have seen before as well as those on my wish list to my instant messenger account. This way when I am in that situation, the lovely ladies that reply to my IM's will typically get the appointment. Even if I haven't been verified by them prior, most ladies on my list have P411, the whole process typically doesn't take more than 10-15 minutes.
Hope this helps brotha! Happy Hobbying.