When did the alternate timeline(s) get formed?

im trying to make a WHH theory. but i need some info about alt timelines. i wanna understand… when did the alt timelines form?

when….ben turned the wheel?
when locke turned the wheel?
when losties went back to 1977?
when daniel told them to blow up bomb?
when juliet woke up at the bottom of the shaft
when the bomb exploded?
or some other event.

also, what is special about the event that made it not happen originally?