Water famously freezes at 32 degrees Fahrenheit (0 degrees Celsius). But purified water, like the stuff you buy in bottles from the store, doesn't have anything but water molecules in it. So there's nothing to kick-start the usual heterogeneous nucleation process.
If you have bottles of purified water, you can pop them into the freezer and leave them undisturbed — no moving, no touching — for a couple of hours. They'll still be liquid because pure water with no nuclei in it freezes at -43.6 degrees Fahrenheit (-42 degrees Celsius). It's now a supercooled liquid, which does indeed sound super cool.
The exact timing it takes for the water to freeze will depend on the size of your water bottles and your freezer, but it will take about two-and-a-half to three hours to get the water to this supercooled state.
It's only after these few hours of preparation that the "instant" part of instant ice happens. But it is amazing. Carefully remove the bottles from the freezer. Then shake one or whack it on the table. Anything can act as a nucleus at this point — air bubbles, a slight dent in the bottle. Any little change will be enough to cause homogenous nucleation.
Once that disturbance is present, the uniform water molecules will become ice so quickly that it looks instant.