Muzzle control is the "best" safety. You know, the old "treat every gun as if it is loaded", along with never putting your finger inside the trigger guard until the shot is imminent. That said, I, personally, don't have a set criteria for safety release, it is dependent upon the circumstances. Generally speaking, if it gets to the point where I have the gun up and shouldered, the safety will be off whether or not the bird is actually in sight. Actually, to me, the act of going off safety any time prior to the actual shot is less troublesome than forgetting to put the safety back on immediately afterwards. I, admittedly, have been guilty of doing so. I suspect I am not the only one. Sometimes it is because of the anticipation of possibly needing to shoot again, sometimes it was probably just being caught up in the moment. One problem with hunting solo so much. I don't do it often, just know I have been guilty of doing so. That is an example of why the other safety rules, muzzle control and finger away from the trigger are so important.
I am sure many of you have seen the video of the FBI agent dropping his pistol when dancing, and the subsequent discharge of the weapon. If you will notice, the gun didn't discharge because of being dropped, it discharged because his finger hit the trigger when he grabbed the weapon.