6 Month old waking at 4am, what should we do?

He wakes somewhere between 4 and 4:30, we are able to resettle, but will then wake up in 30-45 mins. At this point we can often resettle but not always. Aim to start the day at 6am regardless, we never leave the room, it is always dark, no feeding.

Target is feed at 6:30, in cot at 6:45, asleep by 7. He will settle himself most nights with no intervention once he's in the cot.

WW are 2.5/2.5/2.75-3

Not sure whether we should be moving bedtime later or earlier? Is he over-tired, under-tired? Is this just life, for now?!