My little one has the same length 2nd wake window, and he’s been fine on that for the last couple of weeks :) can’t comment on wether it’s healthy or not but it’s working well for us. He couldn’t cope with staying awake any longer in the morning
I wouldn't worry, you can always put him to bed earlier if he needs it until he gets used to the new routine. My LO slept from 9:10 till 9:50 the other day and then was awake until 7pm!!!! She just wouldn't sleep xx
He will probably surprise you, mine adapted really quickly I couldnt believe it. Getting out of the house around 10/10.30 helped me to push it back from 11am to 11.30am and now its 12 which is perfect- being at a class or the park or in a high chair to stretch them out for a while
My LG used to have such long wake windows when we first transitioned to 1 nap only. She was and is perfectly fine and overtime she changed her nap to 12.30 pm.