Hi Im from ON, Canada. The weather this week has had highs of about 15C. I have scotts fertilizer weed control which will control dandelions. Last year I had a ton of them and want to avoid it this year. It says to lay the fertizlizer when weeds are actively growing. Do I lay this down in the next couple of weeks. I see no weeds growing yet, but I just don't want to put the stuff down too late.

Sounds like your weather is about the same as mine in central Ohio.

Our rule of thumb: When "things start blooming" put down the first application.

... so put it down now; but don't count on that to last the season. I give my home 5 treatments per year:
1. Crabgrass prevent in March
2. Weed & Feed (fertilizer & weed control) in April
3. Again in June
4. Again in August (excepting for years that it's so hot we've got burn-out)
5. Heavy fertilizer only in October