Paying staff for previous month

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Hello, 

We are new to Sage Payroll. My team work a month in hand and are paid 15th the following month. I am trying to figure out how to include the timesheets from 1st to 30th (previous month) in the current payroll run. For example 15th Sept - I am paying for 1st-31st Aug. Any help in how I can include the timesheets for this? 

Thanks in advance.