The manual is wrong;
ufopaedia.org tells the correct sweep time at 30 minutes, determined by experimentation on the original game. The OXC devs also have access to a decompiled version of the original game executables to confirm this.
As for the the LOF/LOS difference, you're barking up the wrong tree here if you want to see it changed.
Once of the OXC devs left the project over this exact issue (correction: this was one of the issues that was part of a major contributor leaving) - yes, we get that it's frustrating, but changing it has been deemed outside the scope of the OXC project and in the meantime we try to work around it with things like the new highlighting of objects blocking your LOF.
Edit: Correction by Meridian, see below.