Interesting, and was there any sort of time limit or measures to avoid one person tying up the line for too long?

Yes. You had time quotas, typically.

Downloading files might also be limited by an upload/download ratio restriction, too.

A friend of mine wrote an external program for a particular BBS (what were colloquially known as "door" programs-- software adjunct to the BBS that remote callers could interact with) that allowed you to "bank" your quota time.