Its not long after it turns to syrup... i usually do it in a pan.. so you can judge the thickness. My mom used to let it drip off a spoon, when it started to string out when it was dripping, it was ready for the snow. For anyone whose intertesed Ill be running a facebook page this year ( https://www.facebook.com/MapleSyrupJournal ) , and blogging daily to my site http://howtomakemaplesyrup.com/maplesyrupjournal/ where you can also sign up for email updates.