The practical sequence is assessment notices first, giving an owner the window to appeal to the Board of Revision if the assessed value looks wrong, followed later by the actual tax bill once council has set that year's mill rate through the budget process.
Because the municipal budget and the mill rate are approved together each year, the timing of both the notice and the bill can shift somewhat from year to year, so the date printed on your own most recent notice is a better guide than a general rule of thumb.
If you are planning around a specific due date, the City of Saskatoon's own notice for your property is the document to check, not a fiscal year label borrowed from elsewhere.
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