Once a trade request is sent on Zutopia, you have a fixed window to respond before the request expires and your listing is deactivated.
This time limit applies to both buyers and sellers.
The Acceptance Window
You have up to 60 seconds to accept any trade requests. During this 60 seconds you will be notified four times: initially, then every 15 seconds, at the 15, 30 and 45 second marks. At 60 seconds you will be notified that you were too slow and your listings will be deactivated.