until and by with future tense

[aysaa]

Hello,

Could you please help me because I couldn't get the difference in the sentences I wrote.

I will have been working by 3:00 pm

I will have been working until 3:00 pm

What is the difference between by and until in here?

Thanks....

[5jj]

[Neither sentence is very likely. Are you trying to convey either of these messages;

I will have started work by 3.00pm.
I will be working until 3.00 pm.

?

[aysaa]

-By the end of this year he will have been giving private courses for ten years.

-Until the end of this year he will have been giving private courses for ten years.

Can we put 'until/ till' instead of 'by' in this sentence? I couldn't understand the difference between by and until while using 'future perfect con. tense.

[5jj]

-By the end of this year he will have been giving private courses for ten years.
Until the end of this year he will have been giving private courses for ten years.X.

We use by for actions occurring or being completed no later than a future time point.
We use until for actions continuing up to a future time point.