Why the time goes slower on low fps PC

My notebook is low end and it can't run DR 2.0 at 60 fps.

Then I feel little lag especially in some complex scene. Then I tried to use a timer to record time.

When the time in game is 2:50, my timer's time is 3:10. Huge difference :(

So how can I fix it? Thx!

My notebook: i5 4210h

GTX 960m

I have installed the latest driver.



