Kohl's presently does not have a time limit on returns. As long as you still have your packing slip and/or your receipt, you can make returns any time (a print out of your order confirmation works as well). If you have lost your packing slip and/or receipt they can usually do a receipt look-up by scanning your method of payment and the item you are trying to return. This will not work though if the item you are trying to return has been yellow-tagged in the past, and is now no longer showing up in their system. In that case, you can do a no-receipt return, which Kohl's allows up to 3 times a year per customer. For large no-receipt amounts, they will send you a corporate check in the mail.
Thanks to SD for this information.