The electric car factory needs to be built no matter if it's day or night.
The Tesla Gigafactory 3 in Shanghai, China needs to be completed by the end of this year to at least start production (which will be ramped-up later), but as the timing is tight, Chinese contractors are working 24/7.
***UPDATE: New aerial footage available directly below:
Here is a quick look at the site at night (March 25th 2019) provided by 烏瓦, found and shared by Tesla enthusiast Vincent Yu. It seems that the work at night is performed on a similar scale as during the day. Heavy equipment works tirelessly to complete the job on time.
Though this may seem rather unusual to us here in the U.S., it's actually common In China for large-scale commercial work to proceed regardless of the hour of day, day of the week, weekend or weather conditions. Completion dates in China are rarely pushed back. In fact, most jobs finish ahead of schedule.
Original full video by 烏瓦: