In 1960s-1970s circa the entire DHN Division of today was in ASN Division. Also DDU Division was in ASN Division, thus there were no slacks added. Thus it felt quicker, even upto 2000s when DHN was in ER slacks were not present.
It was only when ECR was formed, time tables started getting more slacks.
Also nowadays more and more PSRs are being added as there is huge illegal mining going on close to the tracks.