I believe a boolean to allow conditionals based on system time could be very useful, and add some interesting new options to skinners. I have no knowledge of how much work would be required to add this to the skinning engine, but I believe the execution for the skinner would be very simple, as stated in the title of the thread.
An example would be <visible>System.HasTime(07:30,19:15)</visible>.
In this particular example, if the time were between 7:30 and 19:15, the condition would come back as TRUE.
Another possibility would be System.HasTime(07:30:00,19:15:00), or System.HasTime(hh:mm
s), which would allow the skinner to specify seconds as well.
This could be useful if the skinner would like a particular action to be performed on every hour for example, or even for previously requested dynamic skins that change appearances based on the time of day. During the day a skin could have one appearance, and then at night it could bring on a more somber appearance, with darker tones and night related imagery.
EDIT: Talking to Jezz_X, it was suggested that perhaps System.IsTime would be more appropriate. In this case, if you used only one variable, it would be exact, such as System.IsTime(12:45) and you could trigger an exact event. If you used two variables, as in my original examples, it would be for something continuous anywhere between those two times.