Button Controllers app:
Global Variables or any of the %var% (%device%,%value%) are not converted when used in strings
This

Will get you this from Pushover
"this is a test on %time% and %date%
BUT if I do the same in Rule Machine
I'll get this from Pushover
This is a test on 09:00 and 05/22/2019
I think I just found my answer...from this page:
The two main differences between Button Controller 3.0 actions and Rule 3.0 actions are,
(1) Button Controller does not have conditional actions, and
(2) It does not support Global Variables.
So no Global Variable in Button Controller app. Got it.