I got to a point where I only offered clients retainer based agreements as I got tired of fighting over hours. Ironically, even when they were being billed by the month they would still try to do these mental gymnastics where they tried to calculate the hourly cost of activities based on rate / hours in a month. It got exhausting. Yes they were often shitty clients. But my point here is, there's a lot of merit in trying to take hours out of the conversation so that I can just get the work done and not have to argue over whether it's going to take me four hours or four hours and fifteen minutes to complete this task.