On-the-go fridge etc

Since I started using the Yogourmet starter kit to make yogurt, I had begun to think about needing one of these cooler bags to shield my box of bacteria friends from the steamy atmospheric heat, from the time it leaves the fridge in the shop to my walk to either the subway station or carpark some distance away. I was told that it is alright to have the box out in (preferably air-con cool) room temperature for 4 hours before it really has to go back into the fridge.