Time limit on main quest - oh gods in hell, no.
I'm not quite sure what the original proposal is trying to accomplish. If I want to rest, I'm going to rest, easy as that.
If you throw random encounters at me like BG, I'm either going to try again until it's successful, or save/reload.
If there are debuffs for resting somewhere, I'm going to deal with them if they're not a real cost, or go back to where I don't get them if it's really necessary.
If you force me to wait until I can rest again, I'm either going to hit the Wait button until I can do it, or go make me a pot of tea while the game is running, cursing that dumb system all the way to the kitchen and back if there is no Wait button.
"Realism" is secondary. This is a game. Every part of it has to work as part of the game. How you do your rest system has nothing to do with being "realistic", and everything with decisions that the player has to make and how you want your game to flow and your abilities to work, and so on. You can write up some pseudo-realistic stuff later to justify it, if you're so inclined.
Edited by Varana, 20 March 2017 - 01:37 PM.