We wanted to use a report to get hours done on tasks for all stories in our backlog.

We didn't find a correct field and used f.e. 'time spent'.
We get here very strange values:
23,99916667
1,998611111
20,99916667
13,99972222
-0,001111111 --> especially this story does have as progress value with 9,5h

What is the reason of this values? What do we wrong? Is it true that we have to set '0' explicitly into field 'time remaining' for each task?
I assumed that if I set the task to 'done' then the time will be calculated correct even the field 'time remaining' is empty/initial.