How do I trade in my old iPhone and Apple Watch?
I wish to trade in my iPhone and iWatch for new models, however will I be without a device?
[Re-Titled by Moderator]
You have 14 days to send in your old device after you receive the new one. See the following from Apple Trade In - Apple
How quickly should I return my trade‑in device?
You’ll have 14 days to return it once you receive your new device.