I wouldn't so much clock watch, but have a set ritual that you follow that indicates it's bedtime. If you can get that happening then you can put him to bed when ever it works, at 2.5yo some children will sleep 13/14 hours at night, some (like my DS2 only ever seemed to manage 10.5 maximum & so I had to often give him a bath at 3 or 4pm to calm him down to get him through to a decent bedtime otherwise he was up for the day at 4am.