I use this one:
It's the Zilla Digital one. I have my day bulbs to come on at 6 am, and my night bulb to come on at 6pm. That way it's a 12 hour light cycle. Though if you only wanted a light for 12 hours, then just plug it into one of the plugs. Yellow is for your day bulbs and blue is for your night bulbs. When yellow are activated, blue aren't and vice verse. You don't have to worry about unplugging or anything. The white plugs have power 24/7 which are where I keep my UTH plugged in.