Perhaps this is done with some informal justification, but certainly never with any formal justification. Moreover, the actual quality of mental existence is completely lost. Scientists don't explain what mental existence feels like starting from the laws of physics. And even if they did, there is no a priori reason to believe that the laws of physics lead one to understand mental existence. The way out of this mire is to say that time is a theory which happens to explain what mentally exists.
Time is that conceptual dimension along which people order memories.
There is no mystery in the relationship between the physical concept of time and mental objects, the relationship is there by definition . What this means is that time is not an assumed concept. The existence and nature of time is not assumed . Rather, it is derived . By constructing a theory of time starting with no time, one is immune from the possibility of contradiction between different concepts of time.