If I'm remembering this correctly, there's an issue with the dates on noticeboards because of time zones. It has something to do with game time and your computer's local time not being in sync, but that issue is on Jagex's end.
Always make sure that you're reading the noticeboard correctly when scheduling events as all dates and times are relative to the UTC time zone when creating an event, which is the time zone Jagex uses for game time. You can't set it for your local time zone.
Hopefully, this issue is fixed in the future, but at least the noticeboard broadcasts it correctly for the day that was set when creating the event.~ Sicariu