Why can boss fights be started while first-timers are watching the cutscene?

[Yumi_umi]

6/8 ppl are i100+
They engage while 3 ppl who are fresh 50 are watching cutscenes = probably almost dead boss by the time the ppl watching finish.
May save seconds minutes idk but whatever works for the majority.

My bad i mean 2 ppl not 3 cuz u know maths... Lol