Posted: 23/05/2013 at 15:38
There are timers around which will do what you want. I have a Gardena timer which can be set for a variety of on times ranging from 1 to 120 minutes. It can also be set to operate on different days of the week rather than every day.
The optimum volume of water will vary depending on weather, aspect, shelter etc. so it is worth experimenting as far as possible in advance to find out what works best. If in doubt less is better than more.