Excerpt from U of MN Extension publication (link below):

"...Time of planting is critical since both optimum shoot and bulb development require a cold treatment. Garlic in Minnesota should be planted in the fall - usually within one to two weeks after the first killing frost (32 degrees Fahrenheit). In northern Minnesota, planting during the third to fourth week of September is recommended, while in southern Minnesota planting around the first or second week of October is recommended. Ideally, roots should be developing and shoots should be emerging from the clove but not above the soil at the time of the first hard freeze (28 degrees Fahrenheit)..."

HTH

Here is a link that might be useful: All about growing garlic

We will experience lack of vigor and yield losses here if we plant either too early or too late. It is unfortunate that we have no way to accurately determine what that actually means from year to year. I have planted in mid October during a warm, late-arriving winter and experienced 40% losses due to shoot freeze-off. During years that winter hits hard and early, plant losses occur only if poorly protected, but yields are down because the bulbs have little chance to establish roots and begin sending the shoots up.

I plant around the 21st of Oct, lay extremely thick mulch down, and cross my fingers. Growers in warmer climes will almost always outyield us here, but I think later is better for survivability. There's nothing worse than looking at shoots above the mulch at thanksgiving time, because you can count on most of them dying in the winter.

Yeah, if the weather reporting industry could just find a way to boost their accuracy! Very tricky business...