Can't answer that question without knowing how you set up your table(s) to record employee time. Do you have one record for each employee for each bi-weekly time period? Is there a date field that identifies each time period in this record?
If so, the basic approach is to perform a find for all records in that time period on a layout set up as a summary report with summary fields to compute the ytd totals. This report can list a single employee's ytd or it can list all employees with a ytd sub total for each employee.
Here's a tutorial on summary reports: