I've got some Yumas & Floridea Ricordia. I target feed them brime shrimps. They can eat a few (2-3) at one go. Ricordia seems to eat more & also more quickly. I switch off all my pumps during feeding. I'll also use a long chop-stick to "glide" any brime shrimps that might have missed their mark towards the ricordia's mouth. They'll swallow it under 2 minutes. If it's farther from the mouth, eg. near the edge of their flap, their surrounding bubbles will still catch the food but they'll take a longer time to transfer it to their mouth. As I've quite a no. of shrimps in my tank, I'll usually keep my chop-stick nearby like a mother hen to fend off any potential "thief". Usually, to kurb this incessant robbing by the shrimps, I'll also feed flakes before I drop the brime shrimps.
I target feed as often as every day but the whole process of fending off "thiefs" can be quite tedious. They can probably survive without this target feeding but I notice that they do grow bigger with this additional source of protein.
Incidentally, from what I read at RC, lighting only provide corals with carbohydrates which gives them the energy for their basic functions however protein is required for growth & this is only derived from feeding. Also, corals feed on zooplankton (ie microscopic animals) & generally don't feed directly on phytoplanton (ie microscopic plants, eg. DTs). Worms (eg. feather duster & other filter feeders) will feed on DTs. If your tank have a balance ecosytem, the excretion or spawn from these worms can then be a very good albeit indirect source of food for the corals.