If this sounds like your week
A timer you can't see is a timer you don't have.
The default places people put a timer — the system tray, a pinned browser tab — are exactly the places you never look. Windows collapses tray icons behind a chevron, and a background tab is one Alt-Tab away from gone. You mean to glance at the time, but glancing requires a deliberate detour, so it quietly never happens.
Where tooling usually breaks
Out of sight really is out of mind.
Every check of a hidden timer is a small interruption: move the mouse, hover the tray, read the tooltip, return to work. So you either break your flow to look, or you skip it and resurface an hour later wondering where the time went. Neither is "staying on schedule" — it's hoping.