like what? she's tired now? ^^ SHould we fast forward to a time when they actually made the place inhabitable?
Aziraphale wants to point out that being ready to work right before dawn will mean she'll be working in the sun, but doesn't want to get himself in trouble. Who knows where that conversation would lead and he's afraid he might get carried away.
"Fine then. I'll just sleep a bit over there, wake me when you're up"
And he proceeds to pretending he's falling asleep.