BY X UNTIL

UNTIL X BY

UNTIL

• An action that will be concluded in the indicated time.
• I have to work until noon.
• Don't tell me anyhting until she gets here.
• She will sleep until 10AM.
• Mary didn't like pasta until she tried it.

BY

• It will determine the beginning of the action or the deadline.
• She has to work by noon.
• They have to hand in the documents by 4PM.
• By the time he arrived I was already sleeping.
• She has to sleep by 8 o'clock.