I have two pairs in my tank and from the get go my Randall's goby and tiger pistol were out and visible all the time. My YWG and candy cane pistol were quite a bit more shy at first but for the last month or so are out quite a bit more.
Like saltwaterfishlover said, I think you will find gobies individually (and all fish for that matter) can have their own personalities that may be completely different than what the 'norm' is for that species. I also wouldn't be too surprised if they disappear for a while at first, but give them time and I'm sure you will see them. My YWG and candy cane went underground for over a month before finally popping back up.