The expression "speed of time" doesn't make much sense, since speed is the rate of change of position with time, and "time" doesn't have a position. Hence it doesn't have a speed.
If you want to know the amount of time dilation at a given speed, it is answered by special relativity. $t' = t\gamma $ where $t$ and $t'$ are the amount of time that passes in the two frames, and
$$\gamma = \frac{1}{\sqrt{1-v^2/c^2}} $$
At low speeds, $\gamma$ is approximately 1, and at high speeds it approaches $\infty$.
To fit with your notion of the speed of time as being the relative rate of passing of time in the two frames, an expression for the speed of time would be $t/t' = 1/\gamma$, which is close to zero at high speeds, and close to 1 for low speeds.
So the speed of time at low speed is equal to 1.