Too late

When is it too late to be late?
If you are a recently deceased Mr X, for how long do you become the late Mr X?
Certainly historical figures don’t count. You don’t go around referring the late William the Conqueror.
Or the late Jesus. If that’s not too debatable.
Is it when you are talking to someone who may not know the guy’s dead? Are you giving him an extra piece of information with your sentence and half expecting an “Oooh I didn’t know he was dead” in response.
Or is this just polite convention?
Is it therefore impolite to omit?
And how long should you be late for?
A month is too short but is a decade too long?
Personally I hate people being late.
They never seem to apologise.