Currently, user rights can have an expiry set (T159416), but cannot be set in advance (to active at a later date/time). I would like to request that the feature be added as it would be of benefit on wikis. In my specific example (enwiki), the event coordinator user right is frequently requested weeks in advance of the event in question, leading to a backlog of (currently) unactionable requests. Having the ability to just set a "start" and expiry date for the user right would save work that administrators currently have to do in monitoring for when the requests can be actioned (day on or before). I imagine that similar scenarios could be found for other projects.
I would imagine that the implementation of this would be fairly similar to that of the expiry, just being its logical inverse and another drop down.