What happens to a timer action when it can't fire on time

I think it’s logic as it is now. But it has not been always the case. It was like that very long time ago, but it changed during a time. Some years ago I wrote a feedback or here in the forum that a Timer fire while the main Thread was busy (not a Thread from the IDE). And I’m nearly sure that Kem answered to leave it as it was.
I have to find the discussion.
But just keep in mind that it may change again.

Edit: What I wrote above may be wrong. It seems that I have a DialogBox change the way it runs. I think it is this forum thread.