Mid march is normal. A week on either side is expected. I remember an early flow one year and it just stopped for about 3 weeks. Saw -28C on the 28th of March. Popped all my taps out of the trees. My sap here has run consistently until about the end of April. Latest I was still making good syrup was Mother's Day. Had to quit then because I was sick of the marathon syrup season and it went from sap weather to +26 within a day.
This is my 22nd year making syrup in Corbeil. I haven't tapped any trees yet.