Their non-response might also have to do with the nature of the questions being asked.
Not at all. Here's the entirety of my email, sent about 10 in the morning:
> Subject: Booking request
>
> I'd like to see Maritsa for one hour at 8:00 PM tonight 30 October at the le Cantlie Suites in room ###.
>
> I can be reached at 1 (123) 456-7890
I also had no response to the same request sent via their website's online booking form.
I did eventually get a response to my email saying to call them after 4 PM. This arrived about 36 hours after my email, 12 hours after I'd left Montreal and 19 hours after Maritsa had left my room. Obviously, I did eventually get in touch with Marika by phone.
Agencies that offer pre-booking via email should probably check their email a couple of times per day. Agencies in general should probably specify on their websites when their phones open. Some agencies are much better about being clear than others.