What is the "pause" rule for dummy play in tournament bridge?
The Laws of Duplicate Bridge do not specifically address the pace of play following the tabling of Dummy, but rather more generally state (my emphasis):


  Law 73(A)(2): Calls and plays should be made without undue emphasis, mannerism or inflection, and without undue hesitation or haste. ....
  
  Law 73(D) Variations in Tempo or Manner
  1. I t is desirable, though not always required, for players to maintain steady tempo and unvarying manner. However, players should be particularly careful when variations may work to the benefit of their side. ....


and


  Law 74(C)(7): varying the normal tempo of bidding or play for the purpose of disconcerting an opponent.


Any unduly or abnormally rapid play from Dummy (ie without consideration of the entire hand) would be a clear violation of all of these mandated Proprieties and Etiquettes, and subject to disciplinary action under Laws 73(F) and 90.

As with all occurrences of irregularities, the appropriate action is to call the Tournament Director as per Law 9.



Updated 2019-01-23

It is possible you are confusing this situation with the skip-bid pause mandated by some organizing authorities following any bid at a strictly higher level than sufficient in that denomination. It presumes that a bid skipping the level is always unexpected, and requires that:


the skip bidder announce prior to his call: "Skip bid; please pause."
the next player to study his hand for ~10 seconds before making a call.


However, except for the Rules guidance above, no such requirement is made following the opening lead and tabling of Dummy, for any organizing authority that I am aware of.