Is transit visa required for exit and reentry in shenzhen airport for 13 hours layover?

Hello,

My parents are coming from Dhaka - Bangkok - Shenzhen - Seattle. They are Bangladeshi citizen & US Green Card Holder. They will have to spend night at Shenzhen airport so are planning to get out from the airport at night, stay at hotel and reenter airport at noon. Will they require visa for staying at Shenzhen for 13 hours?