Ideal syrup weather is warm days, cold nights. The sap rises and falls with the temperature. Once it rises and stays up long enough to reach the buds on the tips of the branches, the chemistry changes and the sap goes bad for syrup purposes, and that ends the season.
As a boy, I used to help gather sap on my grandfathers farm. That was when they used to hang buckets from the trees. You would trudge through the snow and pour the sap into a big tank on a sledge. The men would boil down the sap in big boilers, cook hotdogs in the syrup and drink whiskey deep in to the night as they watch over the syrup. I can still smell the firewood and the maple syrup.