My questions is: Can we use different prepositions using Future Perfect Tense?
Some context. I will have finished my work BY 10 o'clock or BEFORE 10 o'clock or UNTIL 10 o'clock.
I heard that only BY can be used.
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By would mean you intend around 10. Also the lack of an exact conformation means you are giving an estimate.
Before would mean you are saying this will definitely be done by 10. The fact that you are giving a FIXED time means that this is not an estimate. Therefore both if used right are right for referring to future tense.
When you use "until" it is wrong because until is not correct according to the tense of the sentence. But you can use until in this for
My work will not be finished until 10 o' clock
Is the correct way to frame it.