Before making changes to a nap schedule, I always give my dd a few days to see if it's just a phase, or a true need for a transition. If it's been a week or so, you could try lengthening his A time in 15 min increments. Also, while he's experiencing short naps, it would probably help to move his bedtime up so that he can make up for lost sleep. You could try for 7:00 and see how he does. He may be waking at night b/c he's been overtired from the day. Does he wake at night every night? Are the times the same or erratic? Has he had any new developmental milestones such as rolling?