latest on/by Friday

[Tan Elaine]

Submit the report latest by/on Friday.

I think it should be 'on'. Am I wrong?

Thanks.

 

[shannico]

By is the right preposition as you're talking about a deadline, which implies being able to submit a report or a paper over the days prior to the deadline and on day the deadline is up.
If you say on Friday, it means you can only submit your report on that day, as opposed to the days before as well.
Hope it's clear.

 

[bhaisahab]

It would be more natural as: "Submit the report by Friday at the latest".