I think the convo between Hurley and Miles explained the rules of time travel in the Lost universe.
We're viewing events that are relative to the Losties. In their past, they found the hatch, and in their future they blew it up, if we were to go further into that future, they just skip over the entire time they were on the island and resume at the time they left. After they destroyed the hatch, they jumped right back over the time they had already been there.
I think the bomb went off, but because it was on the island, it didn't work like a regular atomic bomb. Who knows what happens when there's a huge division of atoms over a huge pocket of electromagnetic energy?? All it really did was kick them out of 1977.
If I'm Jack, my experience goes like this, I blow open the hatch, get captured by the Others, get off the island via helicopter, return to the island via Ajira 316, crash back in 1977, set off an atomic bomb, get sent back to my current timeline, then I save the island. I'm never sent back to the time I spent on the island.
The point in time that created the paradox bumped everybody over the time period that would've been changed.