Timed watering doesn't work too well in practice.
You don't get an even distribution, so it can take a long time to set up (each time you alter one section, it affects another). I've used the water sensing devices to prevent over-watering but have not been convinced that they work.
The best method I've found is to water into very large trays, into which you stand pots. Watering is more even that way and serious overwatering less likely.
I would contradict that as my system as posted above with careful set up and maintenance worked perfectly for many years watering no less than twenty patio pots large and small.