Faculty can override the default term dates for their course (though students will only be added 7 days prior to the start of the quarter).  To override the term date, they need to click the course settings menu.  Scroll to the term date area and add the new start or end (or both) date.  They MUST tick the box just below the date entry box to make Canvas see their dates instead of the default date ("Users can only participate...").  Then click the blue Update Course Details button.

Note: Dates default to 12:00 am - if students are supposed to have access on the last date, either change the time to 11:59 pm, or set the date to the following day (at 12 am).