Swipe to the right on your chosen device until the green bar is visible and spans at least half of the width of the screen then release.
Tap the green add (+) button to bring up the Timer configuration screen.
Select if you want the Timer to turn the device ON or OFF, choose a time for it to fire then set which days you would like the Timer to repeat on. If no repeat is chosen, the Timer will fire once then be removed. Once you have configured the Timer to your liking, press "Schedule Timer".
Press the back arrow to return to your device list or press the green add (+) button again to schedule another Timer.