It's pointless at the exact moment that the food touches the floor.
Bacteria does not look at it and go "Oh gee, some food to climb on, lets just wait a few more seconds before we do"..... it just gets on with it.
Someone may have just walked in dog poop or other nasty stuff (or just come out of public toilets) and walked on that floor, 5 seconds is not going to make it any less of a yeuch! moment.
p.s. I have 2 dogs, what falls on the floor is not there long.
