How long you usually wait before requesting new winner?

depends on the reason but if the winner has not rendeem wins i usually reroll right when the giveaway ends
also be aware that you can't request a new winner unless if you have a valid reason

If you have a valid reason to reroll (ex: winner didn't activate previous wins, regifting, etc.), you can do it right away.

Huh? If there is a reason to reroll (already has game, etc), right away. If not, you have to give the winner 1 week to redeem the gift.