Viking said:
According to Stefan Kjällman a biologist who did a lot of research on this, it needs to be boiled 25 min and when chopped up 15 min. It´s also important that the water is boiling before you put in the pine needles to keep the vitamin C.
Just done a search of nutritional stuff at home and online and all seem to agree that the water souble vitamins (and Vit C is one) are lost quickly by cooking, especially boiling. BUT, while some of the vitamin C is destroyed by boiling and heat, in the case of vegetables a lot is simply leached from the vegetables into the water, which in the case of pine needle tea would seem an advantage.
It looks then, as though there must be an ideal point in time at which the maximum amount of Vitamin C is moved into the water, but not destroyed by heat.
The other point which authors make is that chopping up vegetabes reduces Vitamin C when cooking, presumably to the water, which again is exactly the idea for pine needle tea. This would seem to support the notion that chopping up the needles makes more vitamin C available to the infusion / tea and would reduce the amount destroyed by heat, as it would go into the tea / infusion more easily, thus reducing "cooking" time.
All this is the science of Vitamin C though and has nothing to do with how the finished tea tastes, so if it works for you and you like the taste, maybe the science isn't the all important thing.