Many lps respond at night to feeding. For example, brain corals, sun corals, etc open up or let their feeding tentacles out at night so you will have better success trying to feed them at night.
Other corals like dendros, rhizos, balanos, and fungias, doesn't really matter. They are open up all day so you can feed at night or day.
Do you have to feed lps? Yes and No. Non photosynthetic lps corals like sun corals need to be fed. Other corals like fungias, candy canes, and maze brains....not really. They are photosynthetic so they can get a lot of their energy from that.......however, they will eat food and feeding them can make they grow faster.
For me, any lps I have that have a mouth and feeder tentacles, I just spot feed every other day. Be careful about water quality.