02/19/2021 (Fri) 19:26:21
What, are you like there right now or something?
The sooner the better, within 24 hours.
Some people used to really panic about it, especially on older firearms where the surface treatment of the metal has either faded with age, or isn't updated, and older barrels that aren't chrome lined. They would bring Windex WITH THEM to the range, or thus the "just pour water down it!" trick was born.
But basically just within the day, soon as you get home. Don't let it sit overnight.