Apart from staying within range, you also must not use afterburners, shoot at enemy ships, or send any comms. It's all common sense stuff - you're supposed to be as quiet and unobtrusive as possible, so you don't do things that attract attention.
(and as for staying in range for about 20 minutes... I highly doubt that. But it certainly is possible for the enemy to take a few minutes to attack - your impatience is precisely what they're counting on )