I'm guessing the timing is because the OP says 2 buses and I suspect that includes waiting time.
For example, my dc's school is (by coincidence, I've just looked at Google) 2.7 miles away. Even in rush hour it takes only 10 minutes to drive generally.
If I was sending them by bus it would take:
10 minute walk to the bus stop. 5-10 minute (depending on traffic) ride into town. Approximately 10 minute wait for another bus (the buses are meant to be every 10 minutes, but at that time in the morning can be up to 20/30 minutes apart, but may well be travelling in convoy!) 10 minute (round the houses) on next bus. 5 minute walk at the other end. 55 minutes. It is quicker to walk.
It would probably be longer home as the bus from our house is only an irregular ever 30 minutes, so she'd almost certainly have a longer wait in town.
OP. It's perfectly doable. in fact to add to the coincidence my younger one's school is 3.4miles away from the secondary. (and at one point I had an infant school to get to as well, which had to be dropped last, as the only child I couldn't leave to wait, and was in the middle of the schools!)
If you drive it's easy. The secondary school will have library open from fairly early and you can drop early. My trip goes: Leave 8:00, drop dd2 at school between 8:10-8:15 depending on how far away from the school I leave her. Drive back and drop ds at about 8:30 to walk into his school. Both are early but not ridiculously so.
I've once not got ds into school on time in three years by that and that was because I witnessed an accident and had to stop.
If you don't have a car, then see if there's a group walking together (a fair number walk from here) or get him a bike if he's competent and will wear, not carry, a helmet. Otherwise get a scooter.
He'll be absolutely fine and probably love the independence after a few weeks.