From your description I'd say you have a canary wrasse and they don't get to but about 5". It's not unusual for them to stay buried for awhile. I'm sure he'll make an appearance soon. Wrasses in general take a while to acclimate. I brought a fairy wrasse home that promptly disappeared. Didn't see him again for almost 2 weeks. Thought he was a goner. But, he came out and has been pretty much out ever since.
They're great fish. Good Luck with him!