It's not really even accurate, as currently they are really not MST, but rather MDT. I would suggest that the label be as follows:

All times are: US/Canada Mountain (GMT-6 Apr-Oct; GMT-7 Nov-Mar)

Changing the timestamp to GMT would in fact substantively inconvenience USA users, as it puts the reset of "Today's Active Topics" at 8pm EDT, a very likely time to be in the middle of a session.