The rules and the boat's practice set out some specific times. Prudent racers advise that there is always time in any "emergency" to clip in. Despite best intentions of skipper, crew and watch captains, though compliance may not be 100%. All crew should carry at least two waterproof light sources (a small strobe and a good flashlight) and a noise source (whistle) at all times.
Clip in. Don't turn one emergency into two.