8am. Same as lawnmowers. It’s nice and neighbourly to wait till a little bit later than that, like 9am, but it’s not realistic for everyone. Some people have kids who’ve been awake since 6 and are climbing the walls and some people need to mow the lawn before they do a bunch of other errands.
It’s a bit like it’s neighbourly not to have loud parties every Tuesday but the council’s noise control guidelines probably talk about excessive noise after 10pm so if the music’s a bit louder than you would like (but not over council guidelines) at 9pm every Tuesday it’s annoying but not unacceptable iyswim.