it's not all the case when both the trains are running on time. sometimes, it is true and get late in the midsection, but slack covers it.
--> i was on-board 12710 on 26th June 2015. we were running 15min late from KZJ, which continued even upto BPP, where 12245 overtook 12710. it took around 5min to clear totaling to 20min. Finally we reached KVZ @ 07.40 with 10min late(because of the slack between OGL and KVZ).