If 0 hours is submitted against a project and any project report, for example Detailed (Task-User) report is run, the report does not show the time submitted i.e. it does not show 0 hours.

This is as per the design. In Smart Interface, it is not possible to show '0' hours entered within a TimeSheet as the application considers it to be a null value and does not save it. Thus, any report does not show 0 hours.

Whenever 0 hours are entered against a Task or Activity, enter a comment. This ensures that an association is created internally between the cell in which 0 hours has been entered and the comment field. Hence, when a report is ran, 0 hours is displayed.