How important is it to keep milk refrigerated all the time?!
very important...the milk will get bacteria and curdle and u can get sick.
If it gets warm at any time, it won't last as long as it would have if it had been refrigerated the whole time. That's all. I don't know how warm it will get, outside the fridge in your house for half an hour. Maybe your house is warmer than mine. Yes, the effect would be cumulative.
I don't think it's really good for you.. How long have you been doing this for? If it's been over a week I think you should throw the milk away. Now, I think you should just stop doing that. (:
Yes keep it refrigerated as much as possible
29 minutes is fine, 30 is deadly poison.
If you want it to taste good.
We used to do that when I was a kid. I am still here.