We pour concrete year round here in the Fraser Valley, but in the heat, cold, rain, extra precautions are needed-Insulated tarps, poly roofs, spray misting to keep cool in heat. The best time is when frost is not a concern anymore, in cool but not cold weather, not in too much heat. March through October are our best months, as long as its not raining, or too hot. Best to worst months usually-April, May, March, September, June, July, August, October, November, December, January, February.