How can I set a coverage end date for a Benefit Plan while assigning to an employee?

Summary

The plan which the employee opts need to end after 25 weeks of assignment.

Content

We have a business requirement that the STD(Short Term Disability) will have a coverage end date of 25 weeks from the coverage start date. While I could find fast formulae for coverage end date. I cannot find a placeholder in the Plan configuration or program configuration to assign them.

Please let me know where can I assign the coverage end date while assigning the plan

Version

20d