It's usually only a thing in bigger projects where we are going to there 6months+ and full time for the clientIf you work 6 hours on project 1 for client A, and 3 hours on project 2 for client B and 1 hour on project 3 for client C - which hours are "overtime"? It makes no sense IMO, they're just billable hours, the client doesn't care what other work you did that day, they're just paying for the work you did for them and an hour of billable work is at a set rate.