Prolonging the time between death and loading of the latest save game

Seems like you want to increase the duration of the death cam, which Death Cam Duration Options can prolong. There's even an insane thirty minute version!

The easiest way is to buy a horse from some stables, and to fast travel to where you want to test from. Then ride the horse off your selected cliff.

You can occasionally survive a fall even if your horse dies, so Bethesda stopped any saves from loading during your decent and only registers survival/death upon the character being stationary.

Enjoy your horse killing and character destroying.