native English speakers, I have something to ask.

that sentence means either "I" (the speaker) will be "there" (the rendezvous point) in 5 minutes or less, or near 5 minutes, maybe 4 or 6 minutes. but if "I" arrived "there" for a lot more than the said time, it means that "I" was exaggerating.

I think it pretty much means that it can go either way. It can be within 5 minutes or it can be after. Most likely it means the latter one, unless the person saying it is ultra reliable. In that case they will be there in 5 minutes or less, unless they get stuck in traffic! Same thing can be said when someone says "just a second" or "just a minute". It's confusing, I know. It confuses the heck out of me and here my native tongue is English! But that's probably because when someone gives me a specific time frame I expect them to be there.

Beautiful cat by the way! "I will be there in 5 minutes." This is 5 min. Not more, not less.

I will be there "in" 5 minutes, implies that the Person, will be there in a time duration that is "around" 5 minutes.It could be a few minutes before or after 5 minutes.So it could be 3/4/5/6/7 mins etc.

Basically means around about 5 minutes. Could be more or less. Says that the person is close to the meeting place.