The 30-day clock starts on the notice date, so a notice that sits unopened for two weeks eats directly into your filing time. Reading the notice the day it arrives, rather than the week property taxes are actually due, is the single most common reason a legitimate appeal never gets filed in time.
The filing itself is a form submitted to the City of Saskatoon along with a filing fee, laying out why the assessed value is wrong, either a factual error in the property record or a comparison to similar homes that sold for less. Evidence, not frustration with the bill, is what the Board of Revision actually weighs.
If you are unsure whether your number is out of line, checking it against real comparable sales before the deadline is worth doing either way. Get your hand-reviewed valuation from Joel Dyck.