Absolutely not. :O) I winter sow here in NS straight into March and April. As a matter of fact, I only start after February 15th most years and am going on my ninth year! Hope you enjoy it.

Some seeds only need a few weeks of -4C to +4C to break dorminanacy. Go for it! Probably should hold off for some annuals & veggies, though.

To quote from Bill Cullina, who wrote a book on propagating native plants of the northeast, and other parts of North America, "Many species will recieve adequate stratification if placed outside before mid-February in New England." Since most of us in Canada are in colder zones than that, WS is not over yet for us. Many native plants need only 30-60 days of 4 degree C. or cooler weather to germinate. Some need 90 days or more and some don't need any. The only time-consuming part of WS is figuring out which seeds are which. If one consults several different germination guides, the information given is often conflicting. That's when I "hem" and "haw" and try to make up my mind when to sow for optimal success. I wish that more of these germination guides were in better agreement. I'm a beginner and I need all the help I can get. Just don't confuse me.

Another source to look at is Gardens North catalogue site.
If the genus you are looking for germination info on is listed she will tell you what it takes to germinate that genus. Unfortunately not all genus are covered.
http://gardensnorth.com/site/
Sharon