Yeah, maybe he's still getting back into routine, I mean his body clock was forced into moving so perhaps it needs some time now to 'lock on' to a regular WU again, either that or he is going to continue to fluctuate his WU time depending on that night's sleep need. I'd think more the former based on him having a strong body clock in the first place.
I know you're still working with the gro clock too which should help to get him into a rhythm. Keep encouraging him to practise quiet time for several mins after WU.
I would not give in to any temptation to give him even a slightly earlier BT at this point, esp with the clock change coming end of the month.