I use the Devcon Aluminum Putty and F2 liquid.
On the Putty, I will wait a full two days (read the instructions). The reason is that the putty (initial bedding) is laid in pretty thick ((3/8 inch) and in 48 hrs will shrink just enough to let the metal pop out of the stock with little effort. The finish on the Devcon looks like someone molded the bedding material right inside of the stock. Nice and slick. Come back in with the F2 liquid (a paint coat) and the fit of material to metal is as close as you can get.
HTHs
RGDS
Bob