Usually just a minute, long enough to get the parts ready to assemble. Some new gaskets come with a bead of it already applied, so time is not ultra critical. Just a thin film is what you want, do not gob it on. When I apply it, I let the stuff flow out of the tube in a thin stream and allow it to lay on the gasket surface in a bead about 1/8" wide once it has flowed out level. Practice first. A fresh tube will flow really fast and may have solvent at the top of the tube. Squeeze that out first.
the stuff will start to skin almost immediately since it has a solvent carrier, but once set, does not dissolve easily. You can clean fresh residue with brake cleaner. It sticks to a clean dry surface best.
There will be some small amount of squeeze out so try not to apply any of it within 1/8" of the main bearing.
-Michael