YANBU at the weekend. Though if they want to make noise, I'd choose lawn mowing over church bells (they ring them every sunday morning near me and I used to live in a single glazed house), tennis coaching a group of kids (I live next to a tennis courts and the tennis instructor has a ridiculously loud voice), and someone riding their motorbike up and down the road for half an hour (I really don't understand why someone did this, it was in the evening when I was trying to put my kid to bed, I felt so sorry for her, it was really warm in her room and you could hear it through a closed window anyway, 8am is preferable to 8pm for this)
That said, if they're super busy and it's got to the point they couldn't walk through it anymore and they can't afford to pay someone to cut it for them then maybe it's okay? Although, I don't know why people love perfectly cut lawns, I would rather have a wild flower garden out back, but alas, landlords are butt heads. Maybe they've got a house inspection by the estate agent and they need to do a last minute emergency moe?
I'd assume 8am on a warm sunday/saturday morning is someone purposely wanting anyone with a hangover to suffer tbh. On a week day, I'd assume they have odd shifts and a complex life that I'd never understand (or they're retired and have assumed everyone's up at 8am) and I wouldn't mind.