I actually think with a 6-6.30pm bedtime that 5.30-6am WU is very reasonable, though I'm sure it doesn't feel that way! But it is 11-12h overnight and I honestly don't think you can expect more. I'd be doubtful that W2S would work in that case as rather than it being a habitual waking it could just be when he is done with night sleep, and nothing will make him sleep longer if he isn't tired. Some LOs are brilliant at super-long nights, my first was like that and I learned the hard way with my second that they aren't al the same! DS was a 5.30am waker for forever, and the only thing that 'fixed' it was actually a later bedtime. Expecting him to do 12h regularly was just unrealistic so we set bedtime at 7pm aiming for a 6-6.30am WU which suited us for getting ready for work etc.
I would be tempted to treat it like daylight savings, push your entire routine forward 1h all at once, nap time and bedtime, and ride it out for several days until the dust settles a bit. What do you think?