Bridge, when does dummy hand get laid down?
After the opening lead has been made by Declarer' left-hand opponent.
From Laws of Rubber Bridge (2014):

Law 41 – Opening Lead, Review, Questions
After the auction closes, presumed (see Law 54C) declarer’s LHO makes the opening lead.   After the opening lead, dummy spreads his hand in front of him on the table, face up, sorted into suits, the cards in order of rank in columns pointing lengthwise toward declarer, with trumps, if any, to dummy’s right.
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