The switch will go in-line with your wiring. Right clicking on it will allow you to set the time you want the current to flow through and when for it to stop. (Possibly two rotatable night-day icons like on the clock for simplicity.) Implementing redstone to have an effect on the timer switch would be useful. I can't decide if having redstone applied should completely kill current flow or make it flow regardless of timer setting. Hmm.
One idea in particular is that you could set up lighting (assuming luminators are coming back?) without wasting energy during daytime and automating the process.
T = Tin | R = Redstone | C = Cable | E = Electronic Circuit | X = Nothing
T R T
C E C
X X X