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.
Roughly speaking, 30 days. Honestly, it would be best to wait that long to seal it. However, most people - and for good reason - don't want to wait that long. It's too easy for there to be something spilled on it. If you really want to do a bang-up job, do your first application of sealant after 48 hours. Then, 30 days later, clean the grout with a toothbrush, using a strong mix of bleach & water.