I suppose one could make a case that if Mass, in its entirety, routinely went for 1:15, then from the beginning to distribution of Communion is likely at the 1:00 mark, and thus, one drinking coffee then going in for Mass would not break the fast. If it is shorter, that becomes more problematic.
In our parish, Mass can run from 0:55 to 1:10, so going to fellowship ahead of Mass could present a problem. Some of the repeat cantor etc, who attend one Mass, then go over to fellowship for a while, then serve in one function or another at the next or later Masses. Usually they are careful of the one hour observance. It’s not clear that Sally average churchgoer would necessarily be that careful, or even think twice about it.