I just use adjustable drippers on an extremely low setting, and leave the water spigot on 24/7. One drip per second is approximately one gallon per day, so you can estimate how much water you're dispensing.

Most timers are either battery-operated, or have to be wound once a day. To me, that sucks, and I don't want to have to route power to the garden system. With the slow drippers, I can leave this for weeks without issue.