Opportunistic feeders, their diet varies from one region to another. In the Antarctic, killer whales eat about 67% fishes, 27% marine mammals, and 6% squids. Killer whales in the Bering Sea (near Alaska) eat about 65% fishes, 20% squids, and 15% marine mammals.
Even though your shower grout looks dry, using it too early or sealing it before it's ready may damage it, leading to premature failure. Most cement-based grouts require a cure time of 48 to 72 hours before applying a penetrating sealer.
And you can start using the shower the day after you caulk. When it comes time to seal the grout, just clean it well and let it dry before sealing. The longer you wait before sealing, the more chance of it getting stained, but just using it for a shower (no food prep) is relatively low risk.