1 - get a speedboat to Lipe and then a speedboat/slowboat to Langkawi.
2- get the regular transport from Bulon back to Pak Bara, get transport down to Satun, go down to the pier maybe 10km south of town to catch the regular ferries to Langkawi.
I'm thinking option 2 is the easier. But it depends a lot on when you are planning to leave the island.
Booking people on Bulon will be able to organise all this - I found the gals at Bulone Resort's little store pretty capable last visit, even though I wasn't staying there.
Ooops Forgot the "how long does it take" bit.
Option 1 depends on connections - the gap between arrival on Lipe and when the next Langkawa departure occurs. Hell, you might have to stay overnight. No problems, Lipe is a good place with a beach for everyone from lively to laid back, and if I was in the area I would make a point of staying more than one night. But maybe you have already seen Lipe, or prioritise it below your other wants.
Option 2. On arrival at Pak Bara you could jump a taxi for the Thammalang pier for Langkawi south of Satun - I'm thinking 40-60 minutes. The budget option - songthaew/motor cycle taxi into La Ngu - big bus or sonthaew to Satun - motorcycle taxi/taxi/songthaew to the pier - may take 3 times as long. Maybe more if you opt for the big bus and one is not due for a while. I wouldn't be surprised if there is now a direct minibus for travellers to the Thammalang pier - ask when you arrive at Pak Bara. The ferries to Langkawi run fairly often - you can check this online but I'm thinking maybe every 2 hours.