The duration of time dilation depends on the relative motion between the observers and their separation in spacetime. The magnitude of time dilation is determined by the velocity of the observers relative to each other and the duration of their relative motion.
According to the theory of relativity, time dilation becomes more significant as the relative velocity between two observers approaches the speed of light. As the velocity increases, time dilation becomes more pronounced, causing time to appear to pass more slowly for the moving observer relative to the stationary observer.
The duration of time dilation can be different for different situations. If the observers are in constant relative motion, the time dilation will persist as long as their relative motion continues. Once the motion between the observers stops, the time dilation effects will cease, and both observers will return to experiencing time at the same rate.
It's important to note that time dilation is a relative concept. Each observer will perceive time dilation from the perspective of the other observer. So, from the point of view of one observer, the time dilation experienced by the other observer will persist until their relative motion comes to an end.
In summary, the duration of time dilation depends on the duration of relative motion between the observers. As long as the observers are in motion relative to each other, the time dilation effects will be present. Once the relative motion stops, the time dilation effects will no longer be observed.