How to configure Timesheet workflow
To configure the timesheet workflow, go to Configuration > Workflow > Add button
Then choose a designation and the target object : timesheet.
The standard validation cycle is the following, but you can modify it as you need :

Validation types
Timesheet validation can be scheduled either weekly or monthly.

Monthly validation : the timesheet has to be completed on the entire month to be submitted.

Weekly validation : the timesheet has to be completed on a whole week to be submitted.

Steps
There are minimum 3 required steps in this workflow :
- One "submission" step: only one validation is required to process the request.
- And 2 "validation" options that get the timesheet out of the validation cycle and unable any modification on it.
- The timesheet can be validated
- The timesheet can be refused