Oh My Time - Time Tracker For Blender (And Pomodoro)
How to reset Timers?
Under Properties in addon chceck box you have options to reset timers in active file: 
Where to find timer?
You will find addon under scene properties:
How To install addon?
Download the .zip file (DON'T unpack it)
go to blender
Edit > preferences > addons > install ( navigate to .zip file) > and enable chceckbox
And then you will find addon under scene properties:
If it's still not working:
Make sure you using newest and supported version of blender.
Chceck if it's installed, remove and try again.
Go to folder in windows: appdata > blender foudation, > sripts > addons > oh my time
and then delete corupted files, and reinstall addon.