A project leader enters time in the timesheet and the approval path of the project leader has one of the approvers as Project leader . After the project leader submits the timesheet, the timesheet gets system approved.
If a user enters time against a project(s) in the timesheet and submits the timesheet, the timesheet gets directed to the project leader(s) for those projects for approval (provided the project leader is part of the timesheet approval path).
In the scenario mentioned above, the user who enters time in the timesheet against the project is the project leader for that particular project and also has the approval path where in one of the approver's is a project leader. In this scenario upon submission, the timesheet approval path finds that the user who has entered time against the project is the project leader for that project and it gets system approved.
If in the same timesheet the user has entered time against other projects for which he/she is not the project leader and if the approval path contains other project leaders in it, then the timesheet will still be directed to those project leaders for approval.