9.11 Good to know — time tracking

Billed entries are locked, by design. The only way back from billed is through the invoice: void it, delete it, or remove the line, and the entries return to approved (§9.5). There is no quiet edit of billed time.
Snapshots everywhere. Rates and the overtime split are fixed onto the entry when it is saved. Repricing a project or an employee is a forward-looking act; last quarter's numbers stay exactly as they were reported.
Overtime off is not overtime denied. With the switch off, the split simply is not tracked — every hour is a regular hour at the plain rate, and no report will pretend otherwise.
Non-billable projects still cost. Their hours count in utilization and land in project margin as pure cost. That is not a defect; it is how internal work stops being invisible.
My Timesheet needs the link. The page shows the week of the employee your user is linked to (§8.4). A user with no linked employee has no week to show — link them, or let them use Time Entries.
A completed project is not a closed book. Its approved time can still be billed and its reports still read; it simply takes no new time (§9.5).