With my department, once I know I'm going to be away for an extended period (on class b/c), I submit a form to our document services section who logs the dates I request off. This section is responsible for notifying officers (according to their schedule) of when they are required for a trial. If I am already booked for court during this time period, as per my dept's policy, my boss is then responsible for liasing with crown and taking care of these conflicts. Usually it is not a big deal for crown to reschedule a trial or ask for a continuance. My partner was bedridden with a bad flu one day and couldn't make court so come trial time crown just asked for a continuance based on the fact that one of his primary witnesses (my partner) was unable to make it. So in this case, crown should attempt to postpone the trial date and failing that, at trial time, request a continuance based on the fact that one of his witnesses is away on military service...one would think there wouldn't be a problem with that.
Anyways, thats just how it works in my department so check with your department policy. It might be an arduous process for dealing with these conflicts, but then again, it might not.