The concept of being in the "middle of the universe" is a bit tricky, as the universe itself does not have a well-defined center. However, we can consider the effects of time dilation between an observer on a planet in our Milky Way galaxy and an observer on a planet in a distant galaxy.
Let's assume that the observer in our Milky Way galaxy is relatively stationary, while the observer in the distant galaxy is moving at a significant fraction of the speed of light relative to the Milky Way observer. In this scenario, time dilation would come into play due to the relative motion between the two observers.
The magnitude of time dilation depends on the speed at which the distant galaxy observer is moving relative to the Milky Way observer. The closer the distant galaxy observer approaches the speed of light, the greater the time dilation effect. However, it's important to note that for intergalactic distances, the speeds required to achieve substantial time dilation are currently beyond our technological capabilities.
Additionally, the presence of gravitational fields can also cause time dilation. If the distant galaxy observer is in a region with a significantly stronger gravitational field compared to the Milky Way observer, time dilation would occur due to the gravitational effects. This, too, would depend on the specific gravitational conditions in each observer's location.
Overall, the actual magnitude of time dilation between observers in different galaxies can vary greatly based on their relative speeds and gravitational environments. Given our current understanding and technological limitations, it is not possible to provide specific values for the time dilation difference in such scenarios.