Setting is mentioned as spring, not winter. Dialogue even mentions "late snow". Entirely possible maple trees could be giving up first sap.
Also, snow on ground in no way implies current ambient temperature is freezing. Cold, sure, but not necessarily freezing. Concrete will set just fine, just take a bit longer. Adding baking soda accelerates the hardening, btw.
Also, snow on ground in no way implies current ambient temperature is freezing. Cold, sure, but not necessarily freezing. Concrete will set just fine, just take a bit longer. Adding baking soda accelerates the hardening, btw.