User defineable timers in the GUI?

Is there a way to have a user configurable timer on any of the GUI/clients?

For instance if I wanted to give the user the ability to create a timer for switching a wall outlet or a lamp? An application might be that they might want to switch on a light at a certain time. Ideally they would maybe want to switch this on based on the local sunset (or using an offset of the sunset). Ideally, I would want the user to be able to define the timing to his liking, without having to go into a rule code and hardcoding the timer into a rule everytime they change their mind.

If you want to let them set the time directly the Alarm Clock example should give you some ideas.

If you want it to be an offset from sunset you can use the Astro binding to get an event sometime before sunset (long enough that the event occurs long before the offset your users may want to use) and use a Number Item connected to a Setpoint on the sitemap. When the sunset event triggers use the Number Item to set a timer in the rule to trigger the light.