Well, the easiest thing would be to use an irrigation timer/valve. Some of these can be connected right to the spigot.

The next choice it to make one using some sort of timer and a solenoid valve, like a washer fill valve. More work and probably not that much cheaper unless you have some of the parts laying around.

Also, if you use 120v house current make sure you use a ground fault interrupter (GFCI). You see these in most bathrooms and kitchens, they have the little buttons. They are designed to disconnect the power in the event of a short circuit - which is what happens when you get electricuted :)

I've gotten an irrigation timer/valve from home depot last summer to use for my vegetable garden on a drip system also sold by home depot.  It runs on 2 AA batteries.  The alleged pressure controlled drips emitters don't work that accurately but it beats having to water by hand every day.  My problem was fertilizing.  The company who manufactured the emitter system supposedly had an attachment that you could place in-line and place a fertilizer wafer in but Home Depot didn't carry it I never followed up over the web.  I think I will check up on that this year to completely eliminate all hand watering.  Although I'm not sure I want to fertilize every time I water.

But another idea would be to use a pump on a timer.  If you had a reservoir with a nutrient solution.  Pump above veges and let it gravity flow through your distribution lines.