Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Saint John to Fort McMurray as you normally would.
Air Canada is one of the carriers that may have flexible change policies. You can use our site to filter for other airlines that may also have this kind of flexibility.
This flight path from Saint John to Fort McMurray was viewed by 16 users in the past month. Keep an eye out for changes in search interest prior to high and low season.