If you do it soon ( like today or tomorrow), just paint it with the flat

Thanks. We'll just paint over today. We are going to do two (maybe even three) coats of flat paint. How long do we need to wait in between coats? Was hoping to knock it off as fast as we can.

It needs to dry, it will tell you on the can. You can speed it up with fans and heaters

You only need one coat of flat over the semi-gloss. 400 sf per gallon.