I would say too soon. Maybe after a year or even two and you have added a lot of coral or other aged media sources that have worms, amphipods, copepods, etc, and they have had a chance to multiply and make a population in the sand and rocks. Valencienna Gobies can definitely eat frozen foods sometimes, but they need to eat a lot of small meals very often. If your sand bed is not mature they will probably get really skinny or slowly starve even if they eat frozen. I started with a very small Valencienna Sexguttata in my new 4 ft setup even after a year and he did get a little skinny at first. But he has now grown and has a nice full flat tummy as my sandbed has matured now that the tank is 2.5 years old.
