Registration on NZ passport

Hello....we will be travelling on NZ passport from Hong Kong to Chengdu and then to Singapore. Would like to use the 72 hours free transit but it says here that if we are staying for more than 24 hrs, we need to register at the local police station. If staying in a hotel, they can do it but if we use AirBnb, do we have have to find a police station and register within 24 hours ? Has someone done this before and is it easy ? Also does anyone know if Leshan is part of Chengdu and can we travel there on transit visa ?