This may seem like an impossible time to beat when you first try the training course but with some practice and pointers it's not that bad. I recommend watching the video as it's easier to explain things like this when it's along with a visual demonstration. Here are some extra pointers though:

A high accuracy will knock off a maximum of 3 seconds from your time at the end of the run, but you don't need perfect accuracy. In the video I used the pistol after the first section to help with accuracy but you can use the MP5 SMG all the way (which you may find easier) and still get the full 3 second bonus.

Turn up your sensitivity a little because the default setting causes it to take a while to move your aim between targets while aiming down sight.

Although I didn't do this during the video a lot of people run to the right at the start and line up the first 2 targets so they can shoot through both of them.

To save time, be sure to press to start the flashbang throwing process before you get to the door you need to throw it through because it takes a couple of seconds for the animation to play out.

When you throw the final flashbang move backwards out of the door leading to the end while you wait for the flashbang to explode and shoot the final 2 targets through the wall as you edge backward toward the finish. You can even run out for a split second while the flashbang is going off then turn and shoot the targets. And shooting them through the wall is probably easier with the MP5 despite the fact that I used the pistol in the video.

Credits To "PowerPyx" For The Vid