Shooting Range: When the timer begins, press the Y button to go into slo-mo and hold the Left Trigger the ENTIRE TIME. The entirety of the challenge will be in slow motion and you should blow past the required 2500 points for the locker key. In fact, I got so bored after I hit 4600 (the targets go incredibly slow with this method) I just let go of LT and let the timer run out.
Chain Attack: When the timer begins, press the Y button to go into slo-mo and hold the Left Trigger the ENTIRE TIME. You won't be able to see the colours of the tiles but they all have the same symbol on them so match them up that way. The second you get at least twelve tiles of the same symbol vibrating, shoot them for points.
With slo-mo enabled, you have all the time in the world to carefully make matches. In fact, I was regularly over 60 seconds shortly after my first few matches. You only need 70,000 points to get the key and then you can let go of Left Trigger and let the time expire, but I advise going past 100,000 for more supplies to make upgrading go quicker.