Should somebody ever say to you “I’ll be back in a jiffy”, prepare to be disappointed. They are woefully exaggerating their ability to travel. A jiffy can actually be describing one of many short measurements of time.
In electronics, a jiffy is the time between cycles of alternating current, or about 1/60th of a second. (if you’ve ever heard an electrical device humming, that’s at the speed of a jiffy)
In computers, a jiffy is the basic “tick” of the system processor. It varies, but is commonly in the neighbourhood of 1/250th of a second.
In physics (of the astro- and quantum variety) a jiffy is specifically defined as the time it takes light to travel 1 centimetre. That would be 0.000,000,000,033,300 seconds.
Jiffy has also been bandied about as another term to describe the Planck interval. (the theoretically shortest possible length of time) That’s about 0.000,000,000,000,000,000,000,000,000,000,000,000,000,000,054 seconds… give or take.
The important takeaway here is that a jiffy, in no way, gives anybody enough time to run to the store and back.