Personally I would never fire up my lawnmower or weed trimmer or anything with a loud engine before 9:00AM, especially on weekends. Just basic, common courtesy to those living nearby who would likely be irritated by the disturbance. Others in my neighborhood clearly don't feel this way, as I've been woken up from a dead sleep numerous times over the years by people who blithely start mowing or blowing or edging at like 7:30. And since I almost always cut my grass and do other yard work around 6:00pm, I know firsthand that it's not really that uncomfortable to be outside at that time of day. Sure it's a bit hot, but way better IMHO than getting up at the crack of dawn working on a yard that's coated with dew and clogs up your mower or trimmer with big clumps of wet grass.