Ernie,
I’d like to know what your experience is. The military pride themselves (and for a long time have done so) on the ability to accurately deliver a task to specific timings. It’s incredibly important in warfare.
With a map, compass and stopwatch, a Time on Target (TOT) could be made within five seconds by most qualified crews. These skills are drilled into trainees prior to converting to their frontline types.
Those skills haven’t changed much since WW2!! They’re as valid now as they were then.
Nowadays, however, on your frontline type you can use GPS and all manner of kit to assist in a good TOT.
If you’re referring to route ops, then crews try to get to destination BEFORE the scheduled time of arrival unless there is a airfield restriction precluding that. Any delay will be due to technical (some of the air transport fleet are about 40 years old and their reliability reflects this; other newer types have been thrashed to bits and sadly are struggling too), loading, weather or ATC issues and normally apparent as a delayed take-off. Sometimes scheduled arrival times don’t reflect the weather of the day, for instance a strong headwind may have a huge effect on timing which may not be accounted for in the published schedule. Once you’ve done your preflight planning, you’ll know a good ETA.
Hope that clarifies things.