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

Solution 1:

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!

Solution 2:

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.