As always, you want to make sure you're neither rushing nor delaying. However, this is not a scramble situation like it would be on second down inbounds. You can wait until the chain crew is within one or two seconds of being set, and then communicate along the lines of...
"Ball's ready, clock's gonna start on my whistle, there's one second left, here we go," tweet-wind.
That communication seems like a short but fair amount of time. Importantly, it gives the players auditory warning so they have an idea of when the whistle is imminent. With just one second remaining, I don't wish to put the players, who are facing away from me, in a position where they have no idea whether their one-second window starts now or 30 seconds from now. A word of preparation, if it's brief, preserves an opportunity for a team that's ready but won't bail out out a team that isn't.