Daily timesheets are most popular where each person enters the time invested on each project every day, the handy comments option can be used to request more information from your employees too.
Often the methodology is based on the employee type. Senior staff who lead teams and are not performing individual tasks can put in time by month instead of the daily timesheet.
Timesheet submissions by month take the least amount of time, but they also give you the least amount of information on how the time was invested, per day or week gives you more information on how time was invested.
Collecting time metrics from all employees will ensure accurate reporting on both effort invested and profitability analysis.