Ok, in like 200-something manga, the timer was turned off after they were able to be seen correct, that means a few things.
1)gantz will kill all of them
2)they will be freed
But again both options are bad for gantz anyways, as mentoned in other theories, hes collecting a army, or for sure trying to kill as many aliens as possible, or there wouldnt be a reason to revive izumi. So if theres anyone with other theroies to what might result in the timer being turned off, please post!