As stated by Christian, in relation to the mission of finding Jin, there is a long journey ahead of Sun and Frank. Although this could mean that it'll take a long time until Sun finds Jin, it most probably refers to the 30 years that must be traveled before they can be reunited.
As established in previous episodes, turning the Frozen Wheel could be Sun and Frank's route to joining Jin in the Dharma timeframe. Also established is the fact that Ben, Locke, and all of the 316 survivors would travel with them. This, of course, opens up the possibilty of the travels not moving directly to the 70's and instead moving to other previously unseen timeframes (Black Rock, Henry Gale, the Statue). Even though, the Frozen wheel seems to be the only way for Sun and Frank to reach Jin (in 2007 Ben has already destroyed Dharma's timemachine), one of my theories would suggest another route.
Regardless of who Jacob really is (my bet is on Desmond), his Cabin exists on an Island that can be moved, can send people bouncing through time, and can kick someone through both time and space to a far off desert. Speaking of time and space, these aren't actually separate things. Space/Time is essentially one thing. To be able to travel through space is to be traveling through time and vice versa. Jacob's cabin has, in front of our and Hurley's eyes, traveled through space, and, if the writers are in fact following correct theory, can also travel through time. In essence, the Cabin, itself, is a time machine. Which means that it's possible that Sun, Frank, Locke, Ben, or anyone for that matter, could use it to travel to any point in the Island's existence.