(No-one commented on the Enochian stuff? Am I just that much of a geek?)
Why did the angel expect you to cut the plant at dawn?
A few things come to mind. For one, the plant is still dormant before dawn, so it’s not like the juices are flowing. Dawn is literally the quickening to life of that plant, and the touch of God. The second idea is that I haven’t had time to sin yet that day if I do something a few seconds into the day. If I cut the plant at dawn over a prayer and can refrain from masturbating for 10 minutes while holding oozing plants and a ritual knife, I can put the poultice into the bag and that’s taken care of. The third reason is simply precedence. Magic rods are usually cut from nut bearing trees, straight branches, and at dawn in a single stroke. It simply works.