Great Wall Excursion during 17 hr layover

Hello! We are arriving PEK at 5 am and departing to Bangkok at 7:45 pm. I'm assuming we will have to clear customs upon arrival. Is 2 hours enough time to clear customs? Also, if we arrive back to the airport by 5:30 is this sufficient time to check in for our connecting flight to Bangkok? Will we have to take our bags with us or will they be ok to be checked through to Bangkok from or origination point?