This is going to sound a little “out there”, but Doc likes the out there theories so I’m going go ahead and post it anyway.
What if the island itself is a giant time machine? What if Ben knows that the island acts like a giant time machine?
Each bearing takes you to different times when exiting the island. We know that going on the wrong bearing is bad, as evidenced from Faraday’s insistence that they head on that certain bearing of 305. Faraday might knows that time is wonky on the island, due to the rocket getting to the island 31 minutes later. He might know that you need a specific bearing, not just to get back to the freighter, but to get to the right time of the freighter. This might be why they arrived a full day later on the freighter when they were flying back in the helicopter. The bearing that Faraday gave them was the bearing they had when they flew into the island, but over a day had passed, so when they flew back, the bearing was incorrect, thus depositing them in the wrong time when they came off the island.
Back to Ben and Michael. When Ben gives Michael and Walt a bearing to get off the island, not only does he know that it will send them back in time, but he knows exactly when they will appear back in the “real world”. What if he sends them back 6 months or so, gets off the island, takes Walt and leaves Michael alone to scream “Waaaaaalt!” for way longer than should be humanly possible.
It’s also possible that Ben, knowing how the island’s time traveling capabilities works, sent Walt way back, like way way back in time to keep him from the Losties.
And just to do a complete mindf*ck, what if Walt is Jacob?