Hey, I'm also an export. Don't stretch if it hurts. Not gonna help. Take it easy and don't do anything that provokes more pain. Anywhere from a few days to weeks or months and you'll recover, depending how bad it is. Once you have the range of motion back, start building strength - and strength through length exercises are great:
- Romanian deadlifts
- Jefferson curls
- back extensions
- Nordic curls 
- QL curls on 45 inclined bench