I am helping my company to test to use odoo v8.0 to create timesheets for developers. 

My question is how the developer themselves could create the timesheet instead of HR person?

As a testing developer account, I had created a demo project and tasks to check, and when I tried to add the timesheet, I just got lost...

When I click "my current timesheet"

It only allows me to add "today" information and submit to the admin account to approve. If I use "my current timesheet" again to create something for the following day, it always gives me an error message said:

ValidateError

Field(s) `date_from, date_to` failed against a constraint: You cannot have 2 timesheets that overlap!
Please use the menu 'My Current Timesheet' to avoid this problem.

When I click" Timesheet Activities" then I could input more activities, but how can submit to admin to approve??

Usually, the developers in my company always fill in the timesheet once per week after the jobs all done. If I can only use "my current timesheet" on that day, it means the developers must do it every day?? Sorry, I am really lost. 

Thanks!