There are the raiders and then there are their raid allies and raid enemies. Although you get a notice about the raid, please do not act upon it. De facto the raid starts when the raiders start to draw their weapons and threat other people with them. At that point anybody can join the fight (without a prior warning). By doing that, you become involved in the raid and you are fair game to anybody who is going to join it. Do not attack people that didn’t join the fight.
Until the timer has ended.