It depends on how you play. A short hard spanking can last as little as 10 minutes. A long session of mixed play and resting can go on all night. And of course, some TOPs and bottoms like to play 24/7 in role - but I am not one of them.
While there are some TOPs that play the session and then push you out, at this stage I would look for someone who will chat with you afterwards. You are bound to have questions. I talk a lot afterwards with younger and newer bottoms. I enjoy it - see how they are exploring their sexuality and feel for pain. So be up-front and ask. If they say "no" then you know they are not for you.
Being a bottom isn't about not having choice - it's about choosing to give up your power for a while once you are comfortable with the choice of playmate you have made. Better wait and have a good time than rush into a disaster. Even if you get out unscathed it will simply fuck your head up...
Vulcan