Travelling Sydney-Guangzhou , internal fly for tour, HK for 2-3 days, return Guangzhou-Syd.

Hi, We am travelling Sydney-Guangzhou on 6 March and doing a tour in Changsha starting on 16 march.
We return to sydney from Guangzhou on 22 march. We will be visiting relatives whilst in China but want to do a short trip to Hong Kong before the tour starts.

If I travel to Guangzhou on 6th, stay one night and travel to HK the next day, come back to Guangzhou within the 144 hours. Is this eligle or are we safer to get a double entry visa.