While JEI and the JSON recipes state that the recipe only takes 5 seconds / 100 ticks, this is not the case. The processing time is still 10 seconds / 200 ticks yet the fuel consumption is halfed (1 coal will only cook 4 items)

I have only tested the stone recipe (cobble to stone)

Mod version: 1.16.5-1.0.0

This is caused by Polymorph