Agree, I don't think Scintilla uses time, I think its just continuous sequences of typing and deleting, as soon as its non-contiguous the undo is broken.
"type type type", "oops", "back arrow back arrow type one character" the undo sequence starts again at that character. Since I have _never_ typed a whole paragraph without having to go back and fix stuff I have never noticed how big the undo can be :grin:.