There is an app which can be used to determine the time of day to eat and fast during Uposata in case this might be useful :
Unfortunately, doesn’t work on the latest Android version
I just bookmarked this link to my homepage:
Not as fully featured, but the calculation is quite reliable.
I use an iOS app called ‘Sol’
I use an app called “LunaSolCal” which is available for Android and probably for iOS too.
With regard to the app author mentioned it is updated now.
The author also mentioned that added uposatha related information has been added.
The author has also got another app: