First, oops - I made a slight arithmetical error..
We start with the gap to the left - if you were to move into that and then immediately move back it would need to be 4 seconds long (i.e. 2 between you and the car behind, and 2 to the one in front). At 60mph (the speed of the vehicles in that lane) that's 352'.
But to move into it to allow someone to come past you means that you stay in it, and in the scenario I described you're closing on the vehicle in front at 5mph.
So how long before the other person has come past you and you can move back out? In this scenario, he is also going 5mph faster than you.
If we assume the starting point of his "passing" phase is 2s behind you, at his speed of 70mph that's 205', so at 5mph he will draw alongside you after 28s. He then needs to build up a gap in front of you before you can pull back out, which at your 65mph is 191' which will take another 26s.
In other words, you'll be in the lane you moved into for 54s before you can move to the right. With a delta of 5mph you will have closed on the vehicle in front to the tune of 396'.
352+396=748' = 228m. Plus, technically, the length of your car.
So yes - I was a few m out (and that's all) with 237m.
And if it's wet you double that to almost 0.5km.
The OP asked me "Are you a lane-hogger trying to justify yourself?", and I'm not.
But I'd bet that he was one of those drivers who has no idea how much space someone needs to his left to be able to pull over for him and not end up driving too close to the vehicle in front and not force the driver behind to drive too close and not have to slow down.