The CAO change of mind deadline is at 5.15pm on Friday 1 July. The CAO says that every year it experiences a surge in last-minute amendments to CAO applications. This is due to a number of factors - for example, more time spent researching courses and the introduction of new areas of interest. In 2015, 56% of applicants availed of the change of mind facility at least once.
It is likely some students may panic about their perceived exam performance and want to change their course choice as a result, but even the CAO itself strongly advises against this.