I'm not a native speaker but I was under the impression that when you want to say that an event concludes on a certain date you can't omit the "on". However, a native speaker told me that having the "on" sounds strange to them, at least in the particular case we are dealing with. The sentence in particular is:
The event begins on Friday evening and concludes on Monday midday.
They say the second "on", following concludes" sounds strange and they would omit it. Can someone explain which one is correct?