It seems to me that people having issues visualizing time-frames in Lost up to season 5 and that's why it is hard to understand FST.
Hokay, for the simplicity sake we will focus on the OT for now. OT was shown in portions; the chronological order looks as follows: Richard episode, pre-DHARMA (1956, Lock talks to Richard ect.), DHARMA times before INCIDENT (most of season 5 in 1974-1977), FLASHBACKS (various times and locations), OCEANIC time (on the island after the Oceanic 815 crash and before the donkey wheel), FLASHFORWARDS and O6 times (season 4-5, off island AFTER THE DONKEY WHEEL and before the comback), AJIRA time (after the comeback and up until Jacob's death), and AFTER JACOB time (well, after Jacob's death and up until now). Now, aside from Locke and Ben (even thou the second one is questionable) Losties, while time traveling or staying off the island, experience their own LOSTIE timeline (do not mistake with OT; and we're not talking about FST yet). Let's take a comparison of Jack and Jin and Sun (she did not flash to 77, and it's kinda important to point out).
Jack's timeline perception: OCEANIC time (100 days I believe), O6 time (3 years), DHARMA time (like a week or so, not major), INCIDENT, and AFTER JACOB TIME (about a week too, isn't it?).
Sun: OCEANIC time (100 days), O6 Time (3 years), AJIRA time (about a week), JACOB'S DEATH, AFTER JACOB.
Jin: OCEANIC TIME (100 days), DHARMA time (3 years), INCIDENT, AFTER JACOB.
So for Jin, Sun, and Jack exactly the same amount of time passed after the Oceanic 815 crash. And consequently in LOSTIES timeline the Incident happens at the same time as Jacob is killed (at least it seems so). Meaning while the events are 30 years apart of real time, if Sun was to ask Jin what happened like a week ago, he'd go like "oh we nuked the island", and Sun would reply: "Nice, we killed Jacob a week ago".
...to be continued
I'm kinda tired and sleepy, and I would like to check my inconsistencies, so I'll update it later. I would also appreciate any feedback.