The concept of the relativity of simultaneity, as described by special relativity, suggests that the perception of simultaneity can differ between observers in relative motion. However, it's important to clarify that this does not imply that individuals can literally live in the past or future from their own perspective.
Special relativity states that the perception of time can be different for observers in relative motion, but these differences are typically negligible unless extremely high velocities are involved. Time dilation effects, where time appears to pass slower for an observer in motion relative to a stationary observer, are only significant at speeds approaching the speed of light.
In our everyday experiences and with the velocities typically encountered on Earth, the differences in perceived time are too small to have any noticeable effect on people living in different temporal reference frames.
Furthermore, time is a unidirectional dimension, and we experience it as moving forward in a linear fashion. We cannot change our temporal reference frame at will or move freely between different moments in time. We are all subject to the arrow of time, experiencing events sequentially in the order they occur.
Therefore, in our current understanding of physics, there is no basis for estimating the number of people living in distinct temporal reference frames relative to our timeline or experiencing different points in time.
It's worth noting that our current knowledge and understanding of the universe may evolve with scientific advancements, and new discoveries could potentially shed light on aspects of time and its perception that are not yet fully understood. However, based on our present understanding, the notion of individuals living in different temporal reference frames remains within the realm of science fiction rather than scientific reality.