When growing with synthetic nutrients, I typically water until runoff and then vacuum it up. 10-20% runoff is what I often aim for. This helps get rid of some of the salt buildup in the medium.
If growing with organic nutrients, I typically let it sit for 15-30 minutes max to see if any gets absorbed back up into the medium. If after 30 minutes there is still water in the saucer, I vacuum it up.