The best time to prune conifers is typically late winter, when the tree is still dormant. There will be some sap flow no matter what the season, because it is an open wound (unless the branches being removed are dead). However, late February-March is probably the optimum time, but it really depends on the winter we have. If it is a mild winter, like this year, then you will want to adjust to earlier rather than later. Maple sugaring happens when the sap runs, so you want to prune before that. It is very much weather and location dependent. I hope this helps!