first the 30 days:   30 calendar days after the estimated or actual delivery date or within the seller's stated returns window, whichever is longer.

and change of mind:

If the buyer is asking to return the item because it's damaged, faulty, or didn't match your listing description, then you need to accept the return. If they've opened the return for another reason, for instance if they ordered the wrong item or changed their mind, then you aren't required to accept the return – however, where possible we always suggest providing a great customer experience.