It really depends on where the fence is located. Most people do not build the fence right on the property line due to the chance they may encroach on their neighbor's property. Even so, they trespass on the neighboring property unless they get permission to enter that property to work on the fence. Because the fence is probably on their property the neighbor on the other side can't paint or clean the fence without permission from the fence owner.
In this case I think the neighbor is being very cooperative in waiting to clean the fence. And they are making an effort to keep the fence appearance attractive.
