The limit is currently 3 hours (we throw the error Duration range 0 - 10800 seconds) but I can increase to 10 hours since that is what our Webapp supports. There are other changes going out so this will go out some time next week.
If you start one zone and go to iOS does it show watering?
I'll have the team look into this.
Thanks for reporting this.
These are new features being built into the platform, but no date on delivery or access through API.
I'll forward this to the product team.
Thanks for the feedback!