To be honest, I would give them more time. it can take a couple days sometimes for the coral to adjust to it's new tank.
__________________ 180g- Mostly BIG fish and some coral. ~80g Nuvo- My coral tank with "happy fish"~ 90g- FOWLR Not the not happy type of fish~ 125g- Freshwater Malawi Cichlids ~10g- Nuvo- The refugees from the Ich of '18
Duncans are hardy little things. Mine did OK...but then I found a sweet spot for them with my flow and they ahve gone nuts. Looking at your tank, there isn't anyway it will get the flow it needs there. It looks like it is in a dead spot. Move it to the other side so the PH's flow can let its tentacles sway in the water. Yes, it has only been 6 hours and it needs time to adjust to your tank. But where it is isn't going to help it out any.