Watching the countdown is something I definately give my crew responsibility for (it's different if one-up of course). I can keep my head out of the boat, and play the traveller to control speed while he can tell me the time left when asked. He also have time to watch the other boats further on down/up the line and the course for significant changes.
Our timer gives a sound signal at 4min, 1min, 30sec and every second from 10 seconds down to the start.