When to eject?

How does a pilot decide when to eject during a battle? Some possible requirements in order to eject might be:

-as soon as you detect an enemy aircraft
-when your radar warning receiver tells you your enemy has a radar lock on you
-don’t eject just because of a radar lock, but eject when your enemy launches a missile at you
-don’t eject just because a missile was launched because you might be able to evade it, but eject when the missile is to within a certain distance of you, say 5 kms
-don’t eject until you actually see the missile with your eyes
-don’t eject unitl the missile actually hits your aircraft, because up until that time you still have a chance of evading it

Surely different airforces give their pilots different instructions on when to eject. I imagine a poor airforce would regard their planes as more valuable than their pilots, and so would tell their pilot not to eject until he’s 100% sure he has no other option (ie when the missile actually hits the plane) while a well-funded airforce would have different rules.

Do different ejection rules apply when the threat is ground-based instead of another aircraft?

I’d like to know more about this topic.