This simple bronze pocket watch was clearly designed by an expert clock maker. It seems to never be in need of a wind-up. In fact, the place where the winding mechanism should be holds a button of some sort. When you press it, time itself seems to go back a couple of seconds. 

Once per day, as a reaction, you can press the button on the side of the clock after any creature has made an attack roll, saving throw, or ability check and make that creature reroll the die. That creature must then use the outcome of the second roll. Only you notice that time was turned back.

Notes: person with impeccable timing