Last June I put in a new mailbox post and four 4x4 posts for a "snow plow" and "vandal" defense and used the Quikrete RED fast set. It set up in about 15 minutes but left the finish of the work for another 24 hours or the next day. Solid as a rock. I would think with the regular Quikrete or similar product you would need at least a day if not more time for it to really be firm or solid. The temp when I used the Red fast set was in the upper 70's F so I know that helped also, and for some dumb reason I used hot water too