when i feed the tank i usually turn off all pumps for about 30mins. This lets the fish and coral get all they can out of the water column. Any leftover food that has sank to the bottom is kicked back up when the pumps turn back on.
it's always a good idea to turn off pumps and skimmers that way the food stays in contact with the animals longer. feed the fish not the skimmer, feed the corals not the sump. 1/2 to 1 hour when I remember
I would personally keep powerheads on at the very least if I was broadcast feeding (but turn off protein skimmer and/or return pump if possible). This will keep more food in suspension and allow normal feeding. However, sometimes I turn off circulation pumps when target feeding.