1 hour would probably be OK without food, but it will differ from person to person.
Best thing is just to try it, and adjust to suit.
I used to do a 40-mile commute in to work from time to time.
It was quite a hilly route, through remote countryside.
I set out around 6, for an 8:30 start at work, so 2.5 hours ride.
I never attempted this without forcing something down my neck before setting out.
It might be a croissant, or a poached egg on toast.
These can be arranged and eaten quickly.
Once I arrived, I usually picked up a bacon roll from the greasy spoon van at work.
I would get up at 5 for a 6 start, but that was not on account of shoving calories down my throat; it was mostly to ensure the coffee had done it's work before I set off.
Not sure how it relates to time-of-day, but I never felt even slightly bonky on the way in early in the morning.
But on the way home I'd have had a perfectly decent lunch but would often take a wobble about 1 hour in and need to nom a fair amount of Jelly Babies in the village just before the hill. That would give me 10 mins or so for the sugar spike to kick in, just as I reached the climb.