It can be difficult to understand the difference between ‘until’ and ‘by’, so read this to help you. (Then write me your own example sentences!)
by + a time means “not later than”
e. g. You must be home by midnight. / Can you finish the work by six o’clock?
You cannot use until with this meaning.
Call me by 3 o’clock. NOT Call me until/till 3 o’clock.
Something happens by a time in the future.
e. g. I will have gone to bed by the time you get home.
Something continues until a time in the future.
e. g. I will stay up until you get home.
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