Transition to one nap? How to know

How did you know it was time to transition to one nap a day? What signs did your baby show? My son sleeps 7pm-630am has done that since we sleep trained at six months. He takes two naps a day but the last two days he has been waking up at 5am. His first nap is from 9-11 and second nap around 2-3. Occasionally he refuses his afternoon nap but not that often. He also has been dealing with Chronic ear infection the last four months so I’m not sure if that’s contributing to waking up early. He seems very tired still when he wakes up at 5am. And he wakes up screaming