I travel to Toronto regularly and a few days before I arrive, I send 2-10 email to the ladies I am interested in seeing, explaining what I am looking for and when, any screening details they ask for etc. I prebook, always.
I get about a 50% response rate from indy's. 75% from agencies. 10% or less from BP.
The thing is, if you can't be bothered to respond within 24 hours, DON'T use email, don't post your email address, go so far as to tell guys not to email. It's a far better solution to say phone or text only.