To me, it seems the most important criteria are the type of bacteria you have on your floor, and how unique it is to the floor relative to the rest of your home/environment.

If you have been exposed to levels of that bacteria that haven't killed you yet, you probably have the antibodies to handle even a 5-minute floor exposure. And for little kids, it's likely that they have already been exposed to it when crawling around on the floor. In fact, they might even be the source of the bacteria on the floor!

Homeless people who pick food out of dumpsters filled with trash build up a tolerance to a lot of different strains of bacteria.