I shoot to plant garlic between Halloween and Thanksgiving, 6-8 weeks before the first hard frost to 2-3 weeks after, but about a month before the ground freezes solid. The goal is to get the garlic in the ground long enough to grow roots (about 1 month), but not so early that warm weather causes the tops to grow. (Raised beds are typically 8 to 13 degrees warmer then the ground). At 4" deep you wont the soil temperature at about 50F. To reach full maturity, garlic needs to be in the ground for about 9 months. That puts harvest time around the end of June into July.
I have three raised beds (4x4) at the bottom of the hill near the creek. They happen to be spaced 4 feet apart. (I am not sure why I put them in that way!) It dawned on me to construct 2 more raised beds, in between the existing beds, which was very easy to do! I dug up the ground and amended it with compost, manure, shredded leaves and kitchen scraps.
Take your seed garlic and divide it into cloves. Plant the individual cloves about 2' deep and 6-8 inches apart. Remember, the bigger the clove, the bigger the garlic bulb next year. Cover with a blanket of mulch (leaves, grass clippings, newspaper etc), about 6" deep for the winter. Come spring, if all goes well, shoots will start to pop up through the mulch!