Bewildering thread.
If the appointment is 18.00 pm, I will be there at 18.00 pm.
If an event requires to be there ahead of time I'll be there with enough time "to make it".
Life (cinema, theatre, concerts, restaurant reservations, flights and trains, ceremonies, medical treatment etc.) waits for noone.
If something happens that prevents me from being on time (= 18:00 pm in the example above), and if I am able to, I will notify the people involved or do my best to make sure they are notified.
There were times when there were no mobile phones.
I had accidents which kept me from being on time as well as running for a phone - shoot me.
I also was involved in other people's accidents and gave first aid which resulted in me being late - again, shoot me.
I regard private appointments to be -5/+10 minutes.
As a host I loathe people arriving more early than 10 minutes.
Rehearsals: it depends on what is agreed upon.
If we agree on starting to play at 19:00, I will show up between 18:30 and 18:45.
More than enough time to switch on the amp, the PA, etc. to get going.
I was half an hour late "for a gig" once - a nightmare.
The car broke down in the middle of nowhere. But this meant, I arrived half an hour later than we agreed to meet at the club. So I was there 2,5 hours time before the doors opened and 3 h before showtime.
2 hours for setup and soundcheck were more than enough.
All this Army/Navy talk of being on time means being late - well, I'm a civilian.