Your understanding is incorrect. Player draws card (the thing they just used a Brainstorm or Jace or some other mechanism to set to the top of their library);
Vendilion Clique is then played, the ability triggers as Miracle is not at instant speed, and the Temporal Mastery is set to the bottom of their library and they get to draw another card. Seriously, Control players have been using Vendilion for a long time now, and coupled with things like
Karakas they can do some fate-sealing quite often.
You are correct about time being the true test if Temporal Mastery is any good though.