Running AuthHub, are there other variables apart from $$OTP$$ and $$MINUTES$$ that can be used in message templates (1)?
Out of the box, AuthHub doesn't provide other variables than $$OTP$$ and $$MINUTES$$ to set in the Message Template. Giving minutes is recognized as a standard and since it's an SMS or e-mail, it doesn't need to accommodate timezones among the others.
Note that the OTP should come quickly to the end user. If not, then there will be a performance issue.
More, it's common usage to have validity minutes as a message. Having precise timestamps will make it trickier to handle the different time zones the end user may be calling from.
Considering all of that, word differently the message template as saying for instance:
"this code is valid until your sign-in time + 5 minutes"