What departure time is counted if flying Beijing to New Zealand but via Guangzhou

Plan to arrive Beijing from Amsterdam 6.15 a.m. July 27, leave 6.30 p.m. July 29 for New Zealand. However the outward flight touches down in Guangzhou for approx 2-3 hours and departs again at 12.50 a.m. July 30th. Both 'departure' times seem to be within 72 hours, but the Guangzhou time is getting close. Am I leaving at 6.30 p.m. July 29 or 12.50 a.m. July 30?
Joe