I fed my sun corals a few hours after 'lights out'. If the polyps weren't already extended I'd feed some of my other LPS
corals mysis shrimp (to get the scent in the water) then wait for the sun coral to 'bloom' (which usually occurred within 10min).
While polyps will disseminate a portion of the nutrition they obtain to adjacent polyps as long as there is interconnecting tissue, feeding each polyp is perhaps ideal. I'd turn off all circulation and feed as many of the polyps as possible (all of them if I were able), one to three mysis shrimp each.
Frequency of feeding: 3-4 times weekly (every other day would be good if you can do it). This coral is non-photosynthetic so it does not require light. I preferred turning off the circulation during feeding because the flow would sometimes wisk the mysis away from the tubastraea's grasp.
The way I fed this coral was somewhat time-consuming (fed each polyp mysis shrimp with a tweezer), which took about 30-45min (however I preferred target feeding over broadcast feeding). For smaller sun coral polyps I'd squirt cyclopeeze directly on them with an eye dropper.
Yellow/Orange sun coral (tubastraea sp.) & branching black sun coral (t. micrantha):