Equipment is revealed (also known as flipping) at the start of a game, after parties are revealed, after player order is determined and ABCs are selected but before the first character acts in the game.
Well, players are sloppy, basically, and careless often, so Upper Deck approved a lenient policy update.
Now, you may choose to reveal equipment any time at the start of the game, and John Fiorillo recommends doing it when you sit down with your ABCs, just to ensure you don't forget the way Don Bota did in worlds Top 8.
Additionally, at any point before the end of a given characters first turn of the game, you may reveal equipment, as long as you don't do so in the middle of an attack or as a reaction to anything.
If the game has started, and you end a character's first turn, you can no longer, for any reason, reveal any or all equipment that character is carrying.
I expect this will be in a document update the next time we get one, but before DMF Vegas seems more realistic than before Realms.
Cheers!
-teh Sig
Level 2 WoW Minis Judge
"Ouch! That was a water elemental!"-CorayThan