In general, perishable foods like milk should not sit out of the refrigerator for longer than two hours. Cut that time down to an hour in the summer if the temperature reaches 30 degrees. After that time frame, bacteria can start to grow.
Of course other factors will come into play, such as has the milk been stored properly and the age of the milk.
Drinking milk fresh and cold is the best way to enjoy a tall cold one.
Here are some tips on how to store your milk properly.