Jason and Dan commented on it as well but it's up to Perez to be ready and attentive to the pitcher by 8 seconds. It doesn't matter that Turnbull had his back turned. The pitcher can do cartwheels if he wants, as long as he starts his delivery by 1 second.
This happened earlier in the season. I forget who it was. Maybe Perez wasn't on the team at that point but all batters should be aware they have to be ready. Doesn't matter what the pitcher is doing.