Most fire halls work a form of 4 shifts. Its a 4 days/6 off 4 nights/4 off 3 days/3 nights 4 off. So starting on a Monday you would work days Monday to Thursday, off until the following Thursday work 4 nights off Monday morning, back to work Friday work days until Sunday, then Monday to Wednesday night off Thursday Morning and start all over again Monday morning. It works out to 42 hours a week. The hours depend on the fire hall, most of them your day shift starts at 0730 or 0800 and work until 1630 or 1700. Nights cover the rest (1700 til 0730). Keep in mind that many places require you to do any major appointments (medical/dental etc) on your days off. You also could have mandatory training on your days off as well.
Some fire halls due to manning issues are working with 3 crews. Some of these halls are working 24 hour shifts (various schedules). At least one fire hall that I am aware of is working a 3 crew shift of 3 days 3 nights 3 off (they still keep the same hours as above, not working 24 hour shifts). That one is a hard one to work. These halls may be working the 3 crews for the summer to help with summer leave/posting season, others maybe working for the considerable future.
Hope this helps.
keep in mind you are on a holding platoon until you get through your QL 3,4,5 courses.
Not really sure what happens if you have pre service & certs (although they recommend having your certs and experience before applying. Then again the aptitude seems to trump that now). I've heard they put you through a semi skilled course.
*If anyone wishes to clarify , you are more than welcome to.*
More info can be found if you dig around here and on the site/link posted up top