Thanks for replying! No sign of teeth!
I only gave it a couple of days trying 2 hours 45 minutes A time. As his self settling and nap duration got worse I thought I was doing the wrong thing by extending him. However based on your reply I will keep trying for longer. Today for example, he was tired after 2 hours 15 minutes A time in the afternoon. This was after a 2 hour morning nap (longer than usual). I managed to keep him awake for 2 and a half hours before his second nap but it was a real struggle. Hoe am I supposed to keep him up if he's that tired? Then he seems OT when I do put him down!