I'm sure that airline staff will be able to help but: all carriers build delays into the stated flight times. The departure time is many minutes earlier than the time they have in the book for push and rotate - but they want you there earlier. Likewise, if they depart late, then the sector time carries 'fat'. Also the given time is from Push to Shutdown.
One simple example, a route that I take often is LTN to IOM and the time is always given as one hour. Actual 'wheels-to-wheels' is 45 minutes unless we are very unlucky with the winds. In this way, they can be delayed and still arrive on time.
Punctuality is seen as one of the critical parts of the operation, particularly for biz folks. So everyone manipulates the schedule to increase the percentage of flights that arrive on time. This has been so successful that all of the UK railway companies have now done the same thing with their timetables.