10 hours of sleep?

My son is 16 months and use to sleep from 630 pm until 6am. The past month he has been sleeping 630 until 5am! He usually takes a 45 to hour and half nap a day. I worry he’s not sleeping enough. Any suggestions on how to make him sleep longer? I’ve tried putting him down later then 630 and he’s still up at 5..530 the latest.