Long enough so the marriage sticks.
Until it's soft enough that it won't put out and eye when thrown with vigor
It should not be cooked, it should be fired raw from peashooters.
and scorched in the flames of hell
Who eats rice at a freakin' wedding?
...still moist enough to eat, but very sticky.
Till the butter melts...:P
You plan to throw COOKED rice on people?