Its better to provide slack @ last leg..whch will nt impact train to slw down in between to cover slack!!
If its on time, it will depart GRRU wthout its schedule impacted...bt if its late, still the slack keep it arrive in-time!!
If the slack was @ ALD-MGS..it would hav slowed down (to cover slack), in case the train report in-time or slight late @ ALD/MGS!!