Use once as a free action: flip a fair coin. Heads: gain 4 seconds on your clock. Tails: nothing but a sheepish flash on your king.
You draft Grandfather's Watch in either mode. Free action: you choose when to use it, and it resolves without costing your turn.
As a item card, it is a one-use consumable, drafted in either mode.
“It runs slow, in your favor.”