HI soupsville and I'd say welcome to BW but looks like you've been around. =) Happy to have you post with us.
What was his previous routine?
How long did you try the later bedtime- consecutively?
It could be a phase as around 18mo, sleep disturbances are common due to either separation anxiety, growing independence and skills, and/or sometimes teething.
Keeping him in bed until at least 6am and using blackout blinds is perfect. Did he always do so well with a long awake time before nap? If you can manage it one day when he wakes closer to the 6 o'clock hr, is push the nap to 12:30 and bedtime to 6:45 for a few days. If it works, then continue to move nap and bt closer to your old routine. He could be a toddler that needs nap capping at 1.5hrs to be tired enough for bed.
What do you think?