I always thought it would be end of the day, but I'm not sure.

  • 2
    No one knows for sure, but where I come from it's most likely referring to the end of Friday. – Hot Licks Dec 8 '14 at 3:21
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    Eg, "We need that work done by Friday midnight" would almost certainly mean the end of the day Friday. – Hot Licks Dec 8 '14 at 3:22
  • Depends whether you are Jewish, Christian, Muslim or otherwise. – Blessed Geek Dec 8 '14 at 7:13
  • @BlessedGeek: Why is it religion dependent? – user541686 Dec 8 '14 at 7:15
  • For Jews and Muslims, the next day starts at evening sundown. Jewish/Muslim Friday starts on Christian Thursday sundown. Therefore, Jewish/Muslim Friday midnite is the midnite following Christian Thursday sundown. – Blessed Geek Dec 8 '14 at 7:17

I would interpret it as the time between Friday and Saturday, and I think most people would, but it's still definitely ambiguous. If you're writing or speaking, try to use an alternative instead:

  • 11:59 PM on Friday
  • The beginning of Saturday
  • At midnight between Friday and Saturday

If someone else says it, it's not a bad idea to ask for clarification. Even though it's more common for it to mean Friday, there are still times when it will mean Saturday, and neither is totally correct or incorrect.

  • 5 years later, but might be helpful for future readers: you should assume it means 12am Saturday unless indicated otherwise, on the basis that Friday midnight refers to a part of Friday night, which is different from its morning. – user541686 Jan 26 '20 at 14:40

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