I don’t know of any way to automatically insert times from a particular time zone using Keyboard Maestro, but as long as you’re using KM8 it’s easy enough to take advantage of the new %ICUDateTimePlus% and %ICUDateTimeMinus% tokens to generate times at the offset of your choosing. Here’s how to replicate the %ShortTime% token with an additional hour added for EST:
%ICUDateTimePlus%1%Hours%h:mma%
For further information, I recommend checking out this post: Getting the date of “next Friday”
and this wiki page: https://wiki.keyboardmaestro.com/token/ICUDateTime