The thing is, there's no cheat or guarantee trick to help you past the 150 seconds mark.
All you need Is a bit of practice and patience.
I will try to help you reach it the way I did.

Stay in the middle-Left of the screen.
(Unless you are being overun ; then retreat but come back to your initial position)
Do not go in the corners or far right
(You won't be able to see ennemies coming from top & bottom)
Dodge. As the seconds go down if it becomes harder to stay in position, then don't.
You need to move arround and dodge as many as possible but try to remain in the same middle- left area.

Always keep your mouse close to your motorcycle, It will aim faster and make it easier for you.

You need to Wave your bullets up and down, do not always aim for the middle of the swarm or you will be overun from every sides. Focus on the closer ennemies first, everytime one comes on top or bottom shoot him as soon as possible then aim back at the mass. You can't spray N pray your way to 150 S you need to constantly aim, remember that!

The title says it all, remain calm and stay focused. Don't waste your time watching the clock, focus on your main character and the ennemies that are the closest.

As I said earlier, there's no trick or cheat but I know some of you just want the 100% achievement thing and will give up after 5 minutes. Don't. You need few practice shots but beleive me you will reach the 150 seconds pretty easily if you take just a bit more time. Thank you all and good luck hope that helps!

Here's my score after 15-20 minutes of gameplay.