Depends. I can hold a grudge a long time, and that is lame and something I would like to change.
For me its moments. Then passes. If I am hurt until there's dialog and disclosing, the healing never begins..
It depends upon how long it takes me to find an opportunity to vent safely, though even in the absence of an opportunity to vent, I think hours covers the longest period of time.
A few minutes. The faster you let go the better.