As far as I know, there is no need for this concept within physics. I understand there are rules ordering cause and effect etc, but these are true of all points in history, not just true at one point that we call the present for example. I don't think the B theory excludes such notions as one point being near another in time, or defined as before or after with respect to some coordinate system.
Also my understanding that the laws of physics are all reversible with the qualified exception of entropy, mentioned above. Anything that physics models going forwards could also describe another possible system with time reversed. It seems to me that all we need to explain entropy is the notion that the universe is not entirely homogeneous and then the common experiences of past and future, such as the inability to remember the future, can be deduced.