I am not experiencing that same issue on my iOS device at the present time but I have experienced the same issue in the past. I was able to change (and save) an existing schedule with no problem.
I did that while connecting both "locally" and via the IntelliCenter servers on my iPhone.
Usually if you just wait a couple of hours and try again, you may find that it will work just fine.
All I can say is that in my experiences, the Pentair web-client as well as the mobile apps are poor quality, not user friendly, "buggy" and not very reliable and YES, they are very frustrating. That is why I have went to the trouble and expense to find an alternate and much more reliable (and user friendly) means of communicating with the IntelliCenter panel. However, this method that I use is certainly not for everyone as it requires additional IT hardware and software.
My only advice to most "average" or "typical" IntelliCenter users when they experience these type of problems with the web-client and the mobile apps are to contact Pentair Tech Support.
Maybe if they receive enough complaints/issues "maybe" they might take some corrective action with regards to their server/web-client issues but I for one will NOT be holding my breath.
r.