Do your best to clarify task details and scope with your customer using the in-app live chat feature PRIOR to accepting the job.
If the hours of the task change you can add these details once the task is marked as complete.
Adjust hours - input the total number of hours (if different from the original estimate)
Again, make sure you let the customer know before the job if you are billing them extra hours. The final invoice will reflect the updated job details, and the task will be 'finalized' through FastTask, which is the last step.