In theory, you should be able to write for hours past the dealine if you treated a hypothetical completely. You can't be penalized for including too much analysis.
While I think I know what you're saying, I'm going to have to disagree with you on this one. "Legal vomiting" can screw up a good exam grade just as much as too little analysis, and if you could write for hours past the deadline, it's either taking you too damn long to figure things out (
or you've failed to distinguish the critical issues from the peripheral ones.
There's no shame in finishing early as long as you've given your best effort. Some people can just analyze and write more quickly. I was usually one of the first people to finish, and it never hurt me. I finished an exam thirty minutes early yesterday, and I still wrote everything I wanted to write.