Well, early is "cedo" for one.
Or, dozens of other PT words I've never seen before:
But let's explore the differences.
Let's say you are expecting a package that will arrive at 9am (09h00), so you get up at 8am which is an hour before.
But, in another case, the package actually arrives at 8am instead of 9am so the package (it) is an hour early.
"It was almost one hour ago" implies that it has already happened. "E' quase uma hora antes" = "It is almost an hour before" which doesn't imply it already happened.
If you want to say "It was almost one hour ago", then say "Foi quase uma hora atra's.". I'm not sure if this is quite clear, so please ask again if it's not.
agreed that your analysis of english is correct. And after daylight savings, one often does say that the clock is an hour behind. In fact, it's the most normal way to say it, though you could also say that the clock is an hour slow.
However, running slow doesn't seem to be one of the possible meanings for the portuguese phrase.
In Portugal Portuguese at least, that's the way it is: use ser to describe chronological time (hours, days, months, years...) and not estar. We just have to remember it. If you really want to stretch the logic to justify this, then think about time as something that has "permanent" characteristics = everlasting and nothing or no one will change it, and no need or possibility to prove or disprove it. You'd be happy to use ser instead of estar if you agree with this, right?