Check the can. It should have application instructions on it. I'm fairly certain that the time between coats determines if you sand or not. I used 2 coats on my boat and sanded before paint.
I did one coat of self etching primer only on the bare spots, then I did a coat of rustoleum primer over the whole boat. I did not sand in between coats mainly because I was not concerned about the smoothness of the finish because of the amounts of dings and dents.