If you block your number it won't be answered. For a few reasons most people buy a cheap phone used just for contacting escorts - easily bought with cash in Tesco, for example, and topped up with vouchers also bought for cash in Tesco.
I recommend an hour for the first visit if you can afford it, to increase the chance of a good first experience. Most escorts will accept a booking for the next day, and that is ideal so you can be well prepared. Don't assume that your first attempt will be successful - top escorts are in high demand and some are almost impossible to make bookings with. Book by phone and listen carefully to their instructions - they will usually tell you to confirm the booking half an hour or an hour before, sometimes by text, sometimes by phone, and if you don't confirm you will probably lose your appointment.
Search the site for "newbie advice", and you should find lots. A bit of searching on the site to avoid asking questions that have been answered many times will mean you get fewer smartass replies to your questions.
The most important things are reading their advertisement carefully before calling, making sure you are very well scrubbed everywhere and mouthwashed, treating the ladies politely and respectfully, and being discreet when approaching their place of work.
Good luck.