@BearRabbitPants
but it's nice to sit and have dinner, watch tv, chill out etc with the doors open (as it's hot!) without a noise nuisance in the back ground! And like another poster said, it's light in the mornings at 4:30 but I'm sure people would be pissed off if someone was mowing the lawn then !!
Someone mowing the lawn is a noise nuisance? Give over. What rot. Bet you yell and scream at neighbourhood children enjoying themselves outside in the summer weather too. 
@Joans3rddaughter
For people who work night shifts, their sleep during the day between shifts is constantly disturbed by lawn mowers, strimmers, parcel deliveries for neighbours that are not in. The list goes on. And on. Whats the difference.
This. ^ Plenty of shift workers have to tolerate all kinds of interruptions to their sleep, and have to suffer WAY worse than someone mowing their lawn at 8.30pm!!!
@Mangofandangoo
I'm almost certain that everyone on this thread that saying it isn't too late doesn't have young children. 9pm isn't late but it is inconsiderate, just like it would be to mow it at 8 am on a weekend..
I'm almost certain that most people on this thread thinking it's OK, DO have young children, (or did have once,) and that is why they can see it's utterly ludicrous to moan about it.
How on earth do you and your precious kiddie-winks cope in the summer holidays when there are kids over 8-9 years old, playing out and laughing, and kicking footballs about, and playing cricket and various games around the area you live, til at least 10.00pm?
Don't tell me, you live in a field, a mile from anywhere! But OMG, but what about the cows moo-ing, and the sheep bleating, and what about the birds cheeping??? How DO you cope? 
The people moaning about it are clearly people who don't work. People who DO would be much more understanding of how hard it is to get jobs around the house and garden done, when you have very little free time!!
Quit being so precious and selfish, and be more understanding. It's half eight in the evening FFS, not 1.00am. Get a grip.