I don't think Armstrong needs garbage time snaps. He's not really going to get better doing that.
I think out of the first two games, let's ride Tommy start to garbage time in Game 1, then Game 2, take the #2 guy who already saw some action in Game 1, and throw him out there unexpectedly for an early series.
From just Tommy's standpoint, he gets conditioned for this year to go through a full game, and he also gets that "step away and look at it from the sidelines with the film" breather that can often be a positive for a young QB's development.