TT is correct. When the train runs through the Gangetic plains, a section of India very conducive to higher speeds of trains the train maintains a good average speed; its avg speed till NJP is 60 Kmph, which is quite good. beyond that once you enter deep into NFR extremely heavy rains make high speed operations tough, leading to reduced speed.
Also, this is the beginning. with time as the line bears more monsoon and if the confidence of IR increases they may increase sectional speeds. but for now the designed TT is good.