It's always best to go read the actual municipal code violation, often there's a way out. I've been cited serveral times for workin on my vette, boat or jet skiis outside.
I was lucky enough to find that there was an exception for doing 'ordinary maintenance' sat through mon, or something like that. So I got out of it.
There may be some exception for your lawn, and you may be able to argue it.Not for sure, but it never hurts to read and check.
