Expire windows user (license) after some time according to first login instead of a solid expiration date

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http://serverfault.com – In a project, we have lots of Windows user that have bought licenses for 1 month, 2 month,... 1 year and so... CURRENT SITUATION (WHAT I DON'T WANT): When users are created and added to the OS, a solid expiration date is given. WHAT I WANT: Users' expiration date should be calculated automatically after first login. The user might not need his account right when purchases the license. In another words: When a license is purchased at Jan 1, he should use the license until Feb 1. No matter whether he really logs in or not. He cannot come Feb 5 and begin using his license because that has (HowTos)