Like Maplehill said they start about the time the maples quite. My brother and I tapped some a few years ago and boiled it down to syrup and didn't like it. My understanding from Garth Atherton from Maple Pro is that you can't use as intense heat because the sugars will burn suspended. He goes to Alaska every year to sell maple equipment to the Alaska producers and has found that they had to cut way back on the heat to make a good product, some even finished with a pan similar to a piggyback or steamaway using the steam, It would be a interesting project though. I believe in Alaska they use the Black Birch
Success is not final,failure is not fatal.It is courage to continue that really counts
“I have not failed. I’ve just found 10,000 ways that won’t work.”
– Thomas Edison