The Aer Lingus 0730 dep currently is scheduled for 1hr 30m ,although in Win its changing to 0745/0905' I.e. 1hr20m.
Most airlines review bloc times periodically and if they fail to achieve the published times on a certain % of occasions ,the published times are altered in future seasons.
In fact if they regularly operate off slot ( I think more than plus or minus 15mins) they would be challenged by the Heathrow slot committee.
Before this was introduced some airlines used to publish schedules at different times to the slots actually held .