I can prouldy say that have 1000 Gamerscore for this game. It only took me 2 days aswell.

That's quicker than it took me to get 1000 Gamerscore for LOTR: Conquest!

How do you do the new squad record? I struggle with that

i think it has to be a combination of haste, timing and accuracy when you're storming the place. the best way is to play it over and over again, memorising the locations and directions of flashbangs aswell as where the enemies pop up. If the accuracy is getting you down, try aiming near an enemy and then quickly pull the L trigger again. This will pull the sights towards a nearby enemy - lined up for you to shoot!

I think I managed this with 20.2 seconds, but I had a good enough accuracy bonus to bring it down to less than 20.