Here is the schedule of the 121/122 TN exp. from my 1977 All India timetable. This way, you can compare the original schedule to present one:
===============
121 Dn TN Exp
-----------------
MAS 7:10
BZA...
more... 12:55/13:07
BPQ 18:35/45
NGP 21:23/21:37
BPL 3:21/3:31
JHS 7:10/7:20
NDLS 12:50
==============
122 Up TN Exp
----------------
NDLS 7:00
JHS 12:00/12:10
BPL 15:44/15:54
Amla 19:11/21 (Tech. halt)
NGP 21:32/21:44
BPQ 0:20/0:28
BZA 5:57/6:09
MAS 12:35
=============
So, 29 hrs. 35 mts. from New Delhi to Madras Central with a top speed of 110 kmph. And now, with speeds of 130/120 kmph by the Raj/GR/Duronto, the running time has been brought down by a mere hour and 15 mts. That is why the Tamilnadu is a legend!