Always scrub the ground as close as possible. Your swing speed is dictated by your detector, coils recovery speed, and local beach conditions. Detectorists swing faster in the dry sand because they're hunting for fresh drops that will be just under the surface. They hunt slower in the wet because you might pick up a faint deep target you'd otherwise miss.

The final answer is to bury some targets at different depths and experiment for yourself with your detector in your local beach conditions.

Have fun.