Yes, you're supposed to be off by noon on your off day. Sometimes it doesn't happen... Maybe I was lucky, but I almost always got home early that morning or late the night before.
Everything else depends on your specific terminal. You might be on extraboard for a few months or a few years. What terminal are you hoping to get on at?
I'm out of Memphis. Big terminal. Lots of runs and lots of drivers. Probably 40 or 50 on extraboard. If you started now you'd leave on Thursday night. You might be able to get a run in 3 or 4 years and then it'd be really low miles. I'm lucky I started when I did.
Other terminals may be better, but I can't speak for them.
You're doing the right thing by asking these questions now instead of getting disappointed later.