That's right for the grass to get a good start, but you can dig over the area now and give the cold weather over the next few months chance to break up the soil lumps. linky
you don't want to leave prepared soil open for very long. the wind will blow away a lot of the good airy stuff, leaving you with rocks and hard clumps. uncovered loose soil will also accumulate weed seeds and various toxins which lower the pH. ideally you want to backblade the existing dirt and top up with new soil the week before you lay sod. and the OP has a molson canadian avatar, so i'm assuming his lawn is frozen right now.
Thanks for everyones answer. I will be using this thread when the time comes around to start growin the grass. And yes the lawn is frozen right now. There is a huge mountain of snow. I wont be moving in untill April 1st. The snow should be all melted by then
