Mathematical physicism (to coin a phrase) about time is the view that the only truth about the nature of time that is accessible to us is what mathematical physics teaches about time. Bergson, in Creative Evolution, gives what seems to me to be a pretty good argument against this view which I want to give in the following form: Consider the hypothesis that all events, whatever their t coordinate might be, are in fact simultaneous, and the t coordinate simply describes the location of the events along a fourth spatial dimension. This hypothesis is fully consistent with all of mathematical physics. Hence mathematical physics fails to tell us the nature of time, because it fails to distinguish time from space.
The argument does, however, presuppose that time is irreducibly different from space—otherwise the accusation that mathematical physics fails to distinguish time from space would be moot. Bergson does, of course, accept this assumption. I am sceptical of it myself.