well, my friend did the tour about two weeks ago, the shop was open, albeit not so well stocked. but then she went in with one of the managers so maybe they did her a favour.
in any case - you can show up at the gate and ask about the tour. personally, i would not bother until next year (after the second of january) because xmas time is always very busy at brugal. no earlier than 10am and no later than 3pm.