KL TT is not going to be changed since it was published as ZBTT. I am sure NR woud have looked at all these timings and given their clearance to go ahead with the timings only if it was practically doable. Certain allowances might have been given here and there. From railways operations point of view I think they refer to WTT: Working Time Table. That is something which they follow. I am sure it will have slight differences in time at intermediate stns