Timesheet - Cannot find source of huge number of hours

So i have some activities defined, and some users.
One activity shows 3700 hours, real work, for one user associated to it, but cannot find where exactly it is set.
So i go to the activity, select Progress, then on Assigment, i see the user, and it has real h 3700 .

How can i find from where it is comming from ?
Maybe in the tables ?

EDIT:
Seems it has something to do with initial planned and real start and end date. They are very big, and it seems that it take the hours per day and calculates that big hour value.
But i see i cannot change those fields.
Hmmm... i think i need to check the manual )