Hm, I'm a native speaker, and I don't think I would use that phrase now, because it is confusing even to me. https://thewordcounter.com/meaning-of-hot-minute/ I think their explanation is pretty reasonable. My understanding (I'm old) is that a "hot minute" means a short time. If a waiter says, "I'll get to you in a hot minute", it means it may not be exactly a minute, but it should be fast. To me, saying it's a hot minute means still means "a minute", but that many things are happening at the same time. It's not that I'm waiting around doing nothing. I'm rushing to get there. I've never heard of it used as "a long time", but apparently other people do... This is slang. Generally, I would avoid using this in my own speaking and writing.

It'll depend on context, like if you haven't seen an acquaintance in a long time, someone could say: 'it's been a hot minute,' or just 'it's been a minute.' It's ironic usage because it's an obviously incorrect, opposite statement. This would be slang usage, like I would maybe expect frat bros to use this expression. Whereas if you're actively interacting with a person, and they are going to rush off quickly to do something (answer the phone, do a task, etc) they could say 'be back in a hot minute," or just "be back in a minute." This is more like a direct usage of the expression...adding 'hot' is just a slang/stylistic element to the phrase.

Yes.