Time sheet can be auto filled with hours pre-defined by your admin staff when it is set to do so from the Teams beta or a App setting.
To enable the auto-fill from Teams beta, select the team on the left column (the selected team is highlighted in blue) and turn the 'Record Timesheet' toggle button ON. After confirming that the colour of the button is changed from black to blue, click 'Save' button at the top right corner.
TIP: Please remember that the 'Record Timesheet' option is saved for the days specified in 'Remember Team' of the week which contains the date specified in the calendar. If you select a Monday in the calendar, M, T and W for Remember Team and 'Record Timesheet' is turned ON, the setting is saved to the same teams existing on M, T or W. If the same team do not exist in either of the selected days, then a new team will be created.