My understanding is that the earliest copy of Daniel dates to late 2nd century BC–4QDANc. In Dr Peter Ruckman’s “The Book of Daniel” he mentions that there is a copy dated to 180BC. I have heard others claim that we have copies by 200BC at the latest, but I cannot find any evidence for this. Dr Ruckman has a phD in religion–whatever that means. I don’t know that he’s consiederd a serious scholar.