Each player skips their untap step.
At the beginning of each player's upkeep, that player simultaneously untaps each tapped artifact, creature, and land they control and taps each untapped artifact, creature, and land they control.
10/4/2004 This card still affects players when it is tapped.
8/1/2008 Skipping the untap step means that phased out cards won’t phase in, and permanents with phasing won’t phase out.
10/1/2009 You can tap lands for mana before Sands of Time toggles your permanents. The mana you gain is in your mana pool during your upkeep step, but will disappear before your draw step if you don’t spend it. You cannot save it to be spent on the card you will draw this turn.