I suppose it all depends on what volume of trees you’re talking about. I have 100+ trees that are 10 years and younger. I can currently get them all done in a day in Feb / March. As they get older, I’ll have to adjust and potentially start sooner. I figure the later I wait, the less chance there is for winter injury. But I’m also in Central & Northern WI (Zone 3/4). Warmer climate there is probably less concern here. And also if I want to save scionwood, I don’t need to store it so long.