Jim, this really isn't an answer to your question. This is from June 1936. I do not have any older timetables, though obviously they exist. One of my friends had one from the late 20's I think, but I never got a scan of it. Perhaps someone else will chime in on this if they can help.
FWIW, I imagine that the running times for #1 and #2 didn't change much. What would have been different prior to abandonment of the Prairie City extension would have been that #1 would have continued on from Austin to Prairie usually with a different engine and crew, and #2 would have originated in Prairie with a different engine and crew than used for #2 between Austin and Baker. It seems like in conductor reports from the mid20's #5 and #6 scheduled freights had been eliminated and freights between Austin and Baker or vice versa ran as extras.