An hour or more depending on the relative humidity in the air. Fully rubbed out and spread thinly on a piece of paper.
When I say crispy, I'm being literal.
Some like load the tobacco when it's slightly damp as it seems easier to load, then they let it set in the bowl for a few hours to overnight.
Either way is fine. Common rule would be: drier tobacco can be loaded tighter that moist tobacco. But again, you can always adjust the draw with the tamp IF you start on the loose side.