BOS - HKG - PEK - BOS possible? can I add a day trip to Guangzhou?

Plan to visit HKG from Boston in mid April for 4 days and then fly to Beijing where I will stay for 5 days (depart on the 6th day) using the 144 hr visa free new regulation as I am a US passport holder. Since HKG is SAR, I believe this itinerary is Okay, right? Now assuming this is OKay, I was also thinking of going to Guangzhou for one day (or overnight) while still in HKG (that is, start in HKG then go to Guangzhou (overnight) and then back to HKG) before flying to Beijing. Will this new itinerary present any issues with the free transit regulations?