Does the 2 week trade-in time start when I get the kit, or when I receive my new mac?

I recently bought a new mac, and I'm supposed to trade in my old device. The trade-in info says I have two weeks to send in my old mac, but my new computer isn't supposed to be shipped for 3 more weeks. Does the 2 week time start when I get the kit, or when I receive my new mac? I don't want to send it back until I get my new computer.