More than zero? I don't know. I'm not even sure what a useful unit might be.
But really, if someone is going to kill themself with a gun, they're doing to do it within
hours of getting the gun, not days.
Small delays are effective. Large ones have almost zero added benefit, and as
@PappyM3 rightly pointed out, a lot more than zero harm.
Oh, that's absolutely true. Anyone who really wants to do it, will. Guns are really effective though.
But there are lots of studies that show *small* delays sort out the ones who are going to do it no matter what from the ones who have an acute (as opposed to chronic) bout of suicidality.
A friend who's a social worker works in residential care, and she told me that in facilities where the residents are allowed to have knives, simply requiring them to be stored in the kitchen - which they have full 24/7 access to - rather than in their rooms, reduces self harm by some shocking percentage. Literally the delay of having to leave their room and go downstairs to the kitchen has a real measurable effect.
Interviews with people who jumped off The Golden Gate Bridge, but were caught by the nets, almost universally say they regretted jumping immediately after they started falling and rarely make a second attempt.