HAPPY NEW Lunar Year,,,, NEED YOUR REPLY!

Hi there, I'm a Saudi Arabian passport holder, I've arrived in HK And I got stay permission for 30 days from the airport this morning, But I'm going to SHENZHEN and back again to HK. Can I enter again? I've heard that visa. its not multiple entry.
Do you think it has nothing to do with multiple entry Because I'm going to stay for one day In SZ. then enter HK in the other date. Thank you so much.. Plz reply as soon as possible,