Until/by/up to

[Kanta]

Hello every one.

I'll be there until/by/up to 3 pm.

which preposition is appropriate here?

If all can be used,does sentence change it's meaning by using them separately?

[Mister Micawber]

I'll be there until 3 pm. = I will leave there at 3 pm.
I'll be there by 3 pm. = I will arrive there at or before 3 pm.
I'll be there up to 3 pm. = I will leave there at 3 pm.
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Native English teacher at Mister Micawber's

[Kanta]

Thanks sir.

sir,what's the meaning of ''leave'' here? go or reach

[Beeesneees]

leave - the place that they are at now (so 'go from here').
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Cheers m' dears!

[Mister Micawber]

'Leave' never means 'reach', it seems to me.
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Native English teacher at Mister Micawber's