The way i got mine to open faster was to get a piece of raw table shrimp, kind of smash it so that it is tenderized (this will help release the smell of the shrimp). I would just cut the top off of a 2 liter coke bottle so it was shaped like a dome. Then just put the shrimp on top of the sun coral and place the dome over the top of the coral. This worked really well for me, and made them open much faster when i would bring them home from the store.
i had mine trained to open during the daytime cycle.The bottle method works great.Also when they start to open if you can make sure to feed every single polyp.I had a colony of black sun polyps that started with about 6 heads.I grew it into 20+ in about 2-3 months doing this.Sadly i got an aiptasia outbreak and it destroyed the colony :*(.anyways hope my info somewhat helps