I used to be the Food Safety Supervisor (HACCP)for a meat and poultry corporation for years- There is a scientific calculator where you calculate how long the fresh, chilled or frozen meat can be exposed to higher temps before it becomes a safety issue and cannot be shipped from the plant and must be destroyed. This happens all the time in plants (where meat is left out in transit from one end to the other, or on the shipping dock, or whatever), they just don't want you to know it. The USDA is well aware of this and THEY use this calculator to help determine the safety of the meat (pork, beef, poultry). When this situation arises the plant Food Saftey Supervisor will communicate with USDA on site, and will use the calculator to arrive at a consensus.
To have a scientifically measurable impact, the bacteria have to begin to grow to a certain level before it is even considered a hazard. The baseline is 1 Log. A Log in this case is a microscopic count that demonstrates the colony is viable, and replicating, and left unchecked will become a hazard. The variables are time and temperature of course. The hotter and longer the meat sits, the better rate of incubation you will usually get. A baseline temp is 60 deg F; all meat packing plants are kept at or below 45 F.
So, sitting out on the counter for a couple hours is doing nothing measurable to your meat other than thawing it.
It takes at least 4 hours for the bacteria to even begin to stir from their cold sleep and begin replicating.
I know this goes against a lot of what we are led to believe, but it is fact, and our USDA and meat processing industry follows this scientific model.
Hope this helps!
