Mariah Carey is approaching. The shutdown period of most companies is from 21 Dec to 5 Jan. If you want to maximize the compulsory annual leave then you can plan a trip on any flight search engine like Beat That Flight, Kayak, Skyscanner and Google Flight.
You can do open-jaw tickets if Hainan Airlines has direct routes to the destination. Destinations Hainan Airlines flies from SZX to the EU are Paris, Brussels, Milan, Rome, Vienna, Budapest, Cairo and Israel. Note what day the flight is, like Mon, Tue etc. You then can mix and match the backdate or forward of departure and return to your plan.
For example, $1762NZD
12/19 Dec, AKL > Milan via SZX
05/12 Jan, Rome > AKL via SZX
or $1765
12/19 Dec, AKL > Vienna
04/11 Jan, Vienna > AKL
or $1880
14/21 Dec, AKL > Paris
05 Jan, Rome > AKL
or $2130
14/21 Dec, AKL > Paris
05 Jan, Brussels > AKL
or $2863
17 Dec AKL > Cairo
05 Jan, Rome > AKL
A daytime stopover of about 20 hours in SZX is not covered by Hainan Airlines, as they do not offer free transit accommodation. Hotels around the airport in SZX range from $50 NZD to $300 for a queen-bed ensuite. These options are available if you just want to rest and be prepared for your adventure or office day.
A bit of information about Shenzhen, it is one of the 144-hour visa-free ports and one of the four largest cities in China. It was primarily established due to its proximity to Hong Kong for political and economic reasons. There are no renowned historical places but close enough to the birthplace of Yumcha.
+1 for the mention :D