Assuming the technician is using Fusion splicing to connect the fibers, which they mostly do in my country, then there are strict temperatures to be complied with.
Splicing activity must be done in a very clean place to prevent dust or any contamination that affects the splicing process. The temperature of the place which the splicing process can take place may vary from 15º C to 28º C.
Although the fusion splicing machine can work at temperature between -10ºC and +5ºC and the closure can be installed at temperature between -1ºC and +45ºC, you still need to ensure that the splicing technician work in the optimum conditions to give the maximum efficiency.
Typically in Denmark where i live, they use a heated van, where they take the fiber inside via a special window and then work inside at +20ºC or more.
The splicing box you linked to says in the datasheet, that it can be installed at temperatures from -40 to 85℃, but it also clearly says: "The product components shall withstand storage at temperatures of -40 to 85℃."
Fiber Optical Fusion Splicing Tutorial: https://www.fs.com/fiber-optical-fusion-splicing-tutorial-aid-295.html