Learn English – I came to realise… the meaning of “come +infinitive”

Anger: in BrE

to get cross; to get angry (among many others but not with get)

Anger: in AmE (among many others but not with get) to get mad, to get angry, to get cross

In both varieties of English: insanity is:

To go [become] mad but: to be mad in BrE means to be insane.

Whereas in AmE: to be mad means to be angry.

Minor point of slang:

in BrE, to get pissed means to get drunk. In AmE, to get pissed means to be angry.

I sincerely hope you do not get too confused. As you are most certainly not an absolute beginner, this stuff is right up your alley. :) PS: I am not pissed in either sense, BrE or AmE.

It's all depends on 'context'.

Sometimes we use "have a good one" for a single day (good day)

and sometimes for a longer duration. (Have a good one" [trip])

Let's say you tell me you're going on vacation next week. I say oh wow I'm not going to see you until the end of January. When we finish talking, I say to you "have a good one" I'm telling you to have a good vacation because I won't see you until after you have returned. [think of until we meet again]

A really common use for it is for people who don't know each other very well. They don't know if they'll ever see the person again (but they don't want to say that) so they say "have a good one" (with whatever it is you're going to be doing after I leave you).

So, if I just meet you and we had a short discussion on grammar and it's just ended I'm going to say to you "have a good one" [I don't know you and I don't know what you're going to do after because we didn't talk about that. So it's like saying okay, good luck and enjoy what it is that you're going to be doing now.]

In reference to your question: Most of the time it is used for shorter periods of time but it can also be used for longer periods of time. But it all depends on 'context'.