Since new extend offer fee was introduced seller pays 2% of the BuyNow price when putting an item for sale. This fee does not change whether offer is made for 2,8 or 24 hours. BUT! when seller wants to extend the offer he has to pay the fee once more. This makes offering items for 2 and 8 hours useless. Because offering for 24 hours costs the same fee and you don't have to spend additional money to extend the offer.
So I suggest to remove the fee for extending the offer to make 2 and 8 hours offers viable options again.