Earlier quoted context omitted.
Besides the obvious craziness of keeping track of these things... It's worth noting that some people are just completely shit at timeliness, no matter how important the thing is. I am and so are my a lot of my friends "I'm running 30 minutes late!" often meets a "No worries, I might be an hour". A punctuality obsessed person would hate me.
There may be some people who genuinely have trouble keeping track of time or planning ahead, but 99% of people who are habitually late (myself included at times) are just rude and inconsiderate. Come on, in your own example you provide a white lie to the person and tell them it'll be 30 mins, when you know that it could likely be longer. Why not just say you're running an hour late instead? I suffer from this myself,…
That's just her situation, but I think there's generally something larger at play. Something more like people feeling the need to squeeze the most time out of whatever they're doing right now, even knowing in the back of their mind that they're stealing from the next thing. I think it takes a certain amount of unnatural discipline to think of the current thing and the next thing as time-equal.