I just reported this to support so this is only to warn users of incorrect values being shown.
I just got 2 new Form 3 and, long story short, I found out that this happens:
Every time you cancel a print (at least in the filling tank stage), the dashboard will add that print’s supposed time to the “Hours Printing” statistics on that specific printer and also to the “Completed” prints in the printer’s details.
For example, if you start a print that takes 1 hour and cancel it 5 times before it starts it will show that the printer spent 5 hours printing and completed 5 prints when that’s totally incorrect.
So, if you see your printed spent 100 hours printing it didn’t (unless you never canceled a print in your life).