Ok. If you are doing this mission and get to the point to kill the bosses with Cachino but the man only says "theres no time plapla" Usually this comes if you tell him to wait before continuin the mission.
I found a simple workaround for this. Go to Brimstone part of the casino, upstairs to VIP part and there 2 rooms with red doors, both unlocked. Big Sal and Nero are in the room on the right. I sneaked there in stealthboy, put some dynamite on sal and nero and boom! Mission complete. also as I did it hidden so no one in casino aggroed.
Then I just blew the brains out from Cachino just because I didnt like the man! Got even some karma from it

Just make sure you complete "Bye Bye Love" mission first as it will fail for some reason if you complete "How little we know" as I did.