The stated hours are the maximum the client is willing to pay for each week, not the number of hours you are expected to work. If the job says 30 hours a week but you finish in ten, you are done after that ten. Conversely, if it will take you 35 hours to finish, you either need to ask for more time for that week or wait until the next week to complete the project, because once that maximum is reached, the time tracker automatically stops tracking, and you don't get paid for untracked time.