Husky

There's usually a date and time given at the end of the meeting thread for the raid, or somebody mentions sending out that information in some capacity. The location of the boss room isn't typically publicly known either, unless the scout(s) who find it publicize the map data/information. More often than not, that information tends to be relayed in private meetings. So, nothing is magically stopping people from entering, but there's a good chance that they wouldn't know where the boss room is or don't know the meeting date/time unless they were at the meeting/had somebody tell them.

Then why make it an effort to open it as an OP, only to change it back to PP later. Why not have it as a PP from the start, if the meeting is set to private and only a selected few who's invited know where to go?

It was a PP from the start. I changed it to an OP because I remembered the meeting thread was public/an OP, but changed it back after rereading the meeting thread. Takao only gave out the date/time and not the location, which he said he'd PM to people. So a lot of people had the boss details, but not the location.