Account Expiration limit to 90 days in the future

We have an approval workflow for Contractors that requests approval from their manager to extend their account's expiration date.  This gets triggered any time that the account expiration is changed.  What is wanted is to make certain that the new expiration date is not more than 90 days from approval.  In the approval workflow, we are setting the date to be current date + 90 days.  However, this is not working, what ever date the account expiration is changed to, that is the date that the account expiration is being set to instead of being set to current date + 90 days.

We are using a PowerShell function that converts the Account Expires and the number of days remaining before expiration (used in the approval notification).  Is there a way to set the $Request's AccountExpires to a date that is no more than 90 days out?