Unlike the previous Call of Duty 4 time trial course, this is not purely about speed and shooting. You must also avoid civilians, and have a high accuracy to obtain a bonus, which deducts time from your total course time. To get under 30 seconds, you must hit every single target, and injure no civilians. Furthermore, a higher accuracy such as 100% - 120% will benefit you in saving time. You gain accuracies over 100% by shooting multiple enemies with one round (does not obtain you the other achievements, as they are just dummies).
In the video below I use a Desert Eagle and an M9 - an ideal combination for a fast reload and good accuracy. Run through the course a few times slowly to get a feel for direction and enemy/civilian locations.