In relation to our result, we highlight that Einstein pointed out that the definition of time must be based on the clock measure. So, a timeclock relation must be considered : this hypothesis states that there is a conceptually necessary relation between time and a physical process which functions as the core of a clock, with the consequence that time and the physical process cannot be defined independently . In all the critical analyses of physical foundation of the time, the concept of duration has always been highlighted as the fundamental quantity . A fundamental requirement is the time-clock relation, and we can improve it by considering that a global time coordinate t is the time measured by clocks of these observers; so, t is the proper time measured by an observer at rest with respect to the local matter distribution . In relation to our approach, it is possible to consider that [80]: