luggage deposit in Capial airport beijing

We are arriving at 6am in bejing.Is there any luggage storage where we can left our baggage for 8 hrs? or more? i have read that they are providing for tourist within 72 hrs visa free.Can i enjoy this prevellige? we will be arriving on the 18th 6am (with all airport check more or less 8am we can go) Leaving on the 21st Nov. early 9am is our flight time (so more or less we will be in airport early 5 or 6 am.Since the 72 hrs. visa free i base on what time you were stamped by the immigration am not so sure if i can enjoy this previllage.pls advice.Thanksa lot for the patient