If I did not misunderstand, what you want is that the ulti begins to load when entering the map, or that it is already loaded when entering. If anyone has played expansion 71 since the beginning, which is when this system was implemented, they will remember it.
This used to work something like this, people waited at the door for the ulti to load and then they started to clean the map, in maps like infested and hydra, they were done in seconds, it was not really a good idea, people made a map meant to be hard in seconds, so Sts preferred to fix this as they said it wasn't how they wanted it to work.
I see a lot of old people here, so I don't see any innocent requests here.