no this is not a proper fix uv box so there is no datasheet and manual.Basically this is a friend uv box for nails, but it has a 15x15cm empty space that i can use and the distance is 3-4 cm away from the pcb. So i will have propably to try?
You are pretty much spot on.
With the tubes 10 cm apart and reflective foil behind a would suggest an exposure time of about 5 to 6 min.
Past few years I have had boards from a French maker (cif) which only require 2 1/2 min.
Check on the manufacturers recommendations.