Memory foam mattresses shouldn’t stay in their original packaging for longer than 3 to 4 weeks.
Ideally, you should unpack your Tempurpedic mattress as soon as you receive it. Leaving it in the box for too long could damage the foam.
This material is not meant to stay compressed for long periods. If that happens, it may become less responsive and lose its ability to fully expand. Plus, you risk losing the warranty.