How long can sealed packaged yogurt be out of refrigerator before it goes bad?

Some people would consider the risk of bacteria in food being left out too great to risk eating after one hour. Open Yogurt will separate after 4 hours, and will spoil after 12 hrs at room temp.

Yogurt, though, is produced with bacteria, changing its spoilage dynamic.

If it is still sealed, for example, uncontaminated yogurt has a much longer safe longevity*. However even then you are risking at least indigestion from the higher concentration of bacteria.

If it separates in the container, however, that is a sign it has probably been contaminated, or was not an ideal bacterial mix to begin, and should not be eaten regardless how long it was at room temp.

*Personal experience having eaten yogurt that at different occasions was; 6 months expired, left in a hot car for 1 day, and left in a backpack at room temperature for 2 days; with the only side effects being a change of texture with the hot car, and indigestion from the backpack yogurt. Room temperature is possibly the least safe of the three, based on that.