Length of service determination in Months dervied factor

Summary:

Trying to determine the months of service using a derivied factor

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My requirement is for a frontloaded plan, I need to accrue employee with sick leave having worked for 3 months, 6 months and 9 months. I am trying to use the derived factor with UOM Months and determination rule end of year, but it is accruing during the enrollment start date itself. Help is much appreciated. Thanks

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