I've made a couple appointment requests on P411 with listed providers.  But sometimes it is days (or never) before they login and check.  

So a non-response is passive-aggressive rejection

Look at the girls as small business owners who have no one else to mind the store. Meaning? Some are on vacation, some only check their emails every few days, some have family, civie work, personal things to do, etc so escorting takes a back seat.

I get email notifications. I think there is a setting to determine whether we get notifications or not. Like someone else here said, it depends on the girl and how she handles her business. Me personally, I always get back to someone even it to tell them I'm not interested.

Not hooked, just being considerate by not double booking, only to get the non-response that blows my schedule.  

All levels money is king.

If she has been on the site and hasn't responded to you, move on.

Girls who have Gmail accounts get there appointment request in there Promotions file. This is the file that a lot of junk mail goes into. If the provider does not set P411's mail to go to there Primary inbox they will not know 50% of the time that they have received a request. Contact her by email to let her know you sent a request.

you can do one of two things.  Move on, or use an alternative method of contact.  If she is not checking emails all the time, or logging into P411, there is not much you can do.  If I was in a time bind as you seem to be, I'd be trying other ways to contact her and tell her you have sent her a request thru P411 and gotten no reply.  Personally, I rarely use that method of contact as you never know how often she checks those messages.  I'd use her personal, from her website or profile, email or phone as a method of contact.

Well, sometimes their on-line contact page requires too much information which is why I am paying for P411. Then there is the blurb on contact pages stating "If all this information is not provided, we will ignore your request".