The definition of tin foil hats you have is fine but I think the more literal meaning is more appropriate here... essentially, people who wear tin foil hats generally believe that aliens (or "the government") are messing with our brains:
A tin foil hat is a hat made from one or more sheets of aluminium foil, or a piece of conventional headgear lined with foil, worn in the belief it shields the brain from threats such as electromagnetic fields, mind control, and mind reading.[...]
The use of foil headgear is often based on a belief that such hats prevent mind control by governments, spies, or paranormal beings that employ ESP or the microwave auditory effect.[...]
So, people wearing tin foil hats are expecting mental attacks by aliens/Martians.
Someone wearing an actual helmet would be expecting a physical attack from Mars.
The implication is that, for some reason, now that we "know" Martians exist, they will attack us.
But, the sentence after this one in the article explains why the trade of hats is likely unnecessary:
One NASA scientist says there's a perfectly good explanation for these sightings.
It then goes on to describe scientific explanations for all of the "alien" objects.
Vasavada is alluding to a phenomenon called pareidolia, which is when your brain recognizes a familiar object or pattern even though it's not actually there. It explains why people see the Man in the Moon, Jesus in their lunch, or even a tiny woman wandering around Mars.
The context tells you whether or not N hours ago is precise. I would say that, typically, it is not. To be clear, you could add about to the expression:
about N hours ago.
Otherwise, the context will help you determine that it is precise, or you might add exactly to the expression:
exactly N hours ago.
I don't think your usage of N hours ago is correct. For example, if it's 8:40, and you say something with one hour ago, then I don't think it is perceived as anything between 7:00 and 7:59. Instead, it is understood as 7:40 plus or minus a few minutes. In other words, the approximate interval is centered around 7:40 and it is not the interval 7:00 to 7:59.
As for your particular examples, I don't think there's a rule. You are just going to have to choose what feels best.
If you really want to use some rule, you could round to the closest hour. So if something happened 1 hour and 20 minutes ago, you would round down to 1 hour and say X happened 1 hour ago. So for your first example, you could say 1 hour ago, and for the second, you could say 2 hours ago.
Including something like about, close to, almost, etc also sounds natural. Using your numbered examples:
- I got here about an hour ago.
- I bought this almost two hours ago.
Best Answer
It seems unremarkable to me. One dictionary definition of "understand" is "to accept tolerantly or sympathetically". The reader is presumed to do this and is being thanked in advanced for having done so.