You're missing the point of the hint. You need another facility with a longer build time. You can get this facility without waiting for it to be built by having a different facility leave it behind when you sell it.
Yes but i wanna save the build time.
If General Building 48 days, why build, if i wanna Hangar with reduced build time.
This is the goal: 12 days for General building, when done, overbuild with Hangar and its just 13 days, not 25 or 22. If everything build more than 25 days, then its pointless
Now its only reduced with 4 days, its 12/4 days, but i dont understand why calculate with 1x1 building. Large General Building size 2, as the Hangar.