The DSR do not specify a time limit for the return of goods.
The nearest reference to this is http://www.out-law.com/page-430#Return If, within 21 days following cancellation of the distance contract, the supplier requests the consumer to return the goods and the consumer unreasonably refuses or unreasonably fails to comply with the request, the consumer's obligation to retain possession and take reasonable care of the goods continues until he delivers the goods to the supplier.
If the supplier fails to request the return of the goods within 21 days following cancellation of the distance contract, the consumer's obligation to take reasonable care of the goods ceases at the end of the 21 day period.
Once the goods have been rejected the refund should be made within 30 days. The refund is NOT dependent on the goods having being despatched or received by the supplier.