Just to add a +1 to the OP’s request. Here’s my scenario. I work on a monthly fixed retainer for one of my clients/projects. While I’m allotted a minimum number of hours to meet the requirements of my retainer, I don’t bill for hours I work in excess of that minimum commitment. So, in my case each monthly sub project I create for this client has a monthly cap on the hours I can bill. For example, I have 90 hours for October. My retainer is $9,000. I bill $100/hr up to 90 hours. Anything above 90 hours is gravy (for them 
) and isn’t billable.
It would be great if Klok could accommodate this scenario.