Each provider is different (trite but true). The best thing you can do is spring for TER VIP membership so you can see all the details and read the reviews of any ladies you are considering. You should also look through the "Self Help" section to get and understanding of how this all works. There are unwritten rules that you have to know. Violating them will, at best, insure that you won't get to see the ladies, or at worst get you kicked out of a date. Most of your questions should be answered by your research.
It also depends on what you are looking for. If you just want a quick nut with a beautiful woman or "the best blowjob you ever had", an hour will be more than enough.
GENERAL GUIDANCE...but every provider is different....
Providers will allow multiple pops in an hour (if you are capable). The "services" don't really change, but a longer date allows for more exploration. In a longer date you have more of chance to chat and discuss things you might like to try. As long as it is not something outside the boundaries of what the provider is willing to do, she will try to fit it in.
For your first date, I would recommend booking for 1 hour to "get your feet wet". Like so many other things in life, you will get better with practice. There is a fair chance that your first encounter will not be "amazing" simply because you will be nervous as hell, not sure what to do, and your mind will be too overwhelmed to focus well. Also, you may not have a clear idea of what you want out of this experience yet. After a few dates you will start to get an idea of what is possible and what you want. At that point you can start booking longer dates with either someone you have already seen and "connect" with, or with ladies that you now know enough to be pretty sure you will click with.
YMMV
JB