Because the timesheet is a separate form. Nothing links it to the work, so it is reconstructed on Friday from a calendar and a rough memory of Tuesday.
A timesheet is the set of hours a person logged against tasks in a period, submitted for approval and then costed.
Time logs on the task, which already carries its project, phase and billable flag. Submission is weekly, approval is by the project owner, and approved hours become cost and billable value at once.
A developer logs against tasks as they close them. Friday's submission is a review rather than a reconstruction, and the split between two projects is right because it was recorded when it happened.
It will not track anyone automatically. No screenshots, no idle timers — the hours are what the person says they are, which is what you can defend on an invoice.
Approved hours become project cost at the person's rate from Nest, billable lines for the next invoice in Books, and actuals against the estimate on the task.
Yes, with the date it applies to. Locked periods need reopening.
The project owner, or a delegate. Approval is what makes time billable.
Yes, against internal categories, so utilisation is honest.
Fourteen days, every module, no card. Or half an hour with someone who will run it on your own records and tell you where it does not help.