The travails of A321 VH-VWU today show how (depending on the roster) delays can compound.
It was bang on time arriving at 0910 hours on the 0630 ex YD up to TSV, JQ912, its first for the day. Then it went back down to SYD as JQ913, arriving only two minutes late at 1227 hoyrs. So far so good.
However this larger JQd aircraft then was on JQ517, the 1315 hours lunchtime SYD down to MEL that did not become airborne until 1422 hours, arriving at 1536, 46 behind. Returning to SYD saw it engaged as JQ518, the 1540 hours airborne 70 minutes later for an arrival time of 1820, 75 behind. I haven't checked but there was most likely some holding involved.
It then operated JQ525, the 1750 hours MEL-SYD in the sky at 1942, arriving at 2054, 89 late.
Finally, it's operating JQ532 (2015 hours MEL-SYD) up up and away at 2135 for suggested arrival at 2244, 64 minutes past what the timetable states.
From observation, turnaround in MEL can be extremely slow. Often they're faster in Sydney though what media has stated is a lack of air traffic controllers and sometimes, limits on how many flights can arrive or depart during each 15 minutes (especially in Sydney) can adversely affect airlines.