The process is generally:
- contact the course convenor of the course you intend on skipping - gain approval (or be denied)
- if you are allowed, contact your school office and they will also decide whether they will allow the clash
So given it's the break, it will really depend on how long each of the above responds to your email or phone call.
If it's one hour and if it's unavoidable (for that set of subjects), then they will almost always approve it. You should call them, especially since it's the break and it will be quicker.
I see. Well if it's just 1 hour and if they are both lectures, then you should be approved. If one of them is a tutorial, they will decide whether to allow your clash, but it will almost always be approved.
Don't worry too much about it. Just occasionally look at your timetable to see if they have enrolled you in from their end.