Providing he has somewhere to go out to the toilet first thing and isn’t desperate to get out, he should be able to learn that going for a walk is a “moveable feast”. I have dog walking friends who appear at my door around 9.00.a.m. on weekdays, weather permitting, and we all go for a walk but at weekends or when they are away on holiday I don’t keep strictly to that timing. My two know what my movements mean and often are ready to go for a walk before I am but another time they have sussed out that I am not taking them anywhere and they stay curled up on the settees. Just change the time that you go out, even if it is a short circuit around the streets for ten minutes and break him of the set time habit. As far as I am concerned my dogs have to fit in with my times and are quite adaptable.