The time that it takes for the other car to pass your car is the ratio of the difference of speeds over the length of your car. So if your speed is $1$ and the other car's speed is $2$ and the length of your car is $0.1$, then it takes $1/0.1=10$ units of time to pass your car. It takes the same amount of time in case of speeeds being $60$ and $61$
The only differece is that within the same time period in the first case you moves 10 units of distance where in the second case you moved 600 units of distnce.