By default, the Timesheets module works on a weekly basis, showing as a weekly period when you view timesheets.
You can change this in the Timesheets General Settings where there are four options for timesheet periods:
Weekly
Bi-weekly
Monthly
Semi-monthly
⚠CAUTION: Changing the timesheet period will permanently delete all of the previously entered hours for all employees. You will see a warning when you choose to do this.
Edit period type
Click on your name on the top right, then click Settings.
On the settings menu, click Timesheets, then click General.
Scroll down to Timesheet period, then select your preferred period.
Select a day or date for the timesheet period to begin.
Scroll down, then click Save.
Next time you view timesheets, it now shows in your chosen period.