I think you can add it at any time. I actually use it in my cider to get a bit of sweetness and still be able to bottle condition, and I do that at bottling along with the priming sugar. I just added some to my pumpkin ale, and did that at kegging time too.
Packaged: Vienna Simcoe SMaSH, Mayan Stout, Caramel Quad, Basic Spiced Cider, Spur of the Moment Graff
Recent Meads: Cherry Melomel, Belgeglin, Bochet
Primary: Fresh Simple Cyser
Secondary: Why do I keep this line here...?
Bulk Aging: Mead Day '11 Ginger Metheglin, Cocobochet, Mead Day '12 Traditional (orange blossom) Mead
Planned: Hop Metheglin #3 (NZ hops), Trad. Gesho T'ej