[Plugin: Role Scoper] Dynamic Role Duration Time

So how can I edit this plugin to make the “Role Time Duration” to something more dynamic, like 2 weeks or 1 day? I want to give the users in a certain group access to a page for two weeks, no matter when they registered, but Role Scoper just allowed static/constant dates and times. Is there a better plugin that does what I’m looking for?

http://ww.wp.xz.cn/extend/plugins/role-scoper/