Moment of Silence

• WWizards of the Coast2004-10-04
  Official Ruling
  It must be used before the combat phase starts or it has no effect.
• WWizards of the Coast2004-10-04
  Official Ruling
  If cast on a player when it is not their turn, it has no effect.
• WWizards of the Coast2004-10-04
  Official Ruling
  The player skips their next combat phase this turn (if any). If they manage to have two combat phases, then only their next one combat phase is skipped.

Rulings via Scryfall