Oh I think there is never a bad time for a clock! I think that could easily be added via the environments themselves (such a being trapped in a chamber with water filling up the room). Poisons could be a good one too! Great thought!
Calling a shot is always the better choice in terms of damage, but if you fail the roll you end up having to diminish your Dice twice, which you may not have the resources for (since typically a face off happens towards the end of a delve, or at least after a few other encounters).
And just so you know Im gonna continue to release support for this game, like a Delve generator and a campaign support system (with overland travel mechanics).