For thirty years now, hunting in the mid-eastern and southeastern corner of Sask, getting there around the 25th of Sept, we have pulled out around the third weekend of October for SD and then on home. We generally always have gotten out before the big freeze up. Only a couple of times in those years have be been driven out by the ice and/or snow. Often times, and as a rule, we leave before the big concentration of northern birds (mallards) migrate into the area to stage. (We head down to SD for opening of pheasant season). Consequently, next year, I'm travelling up a week later and staying a week longer, skipping the pheasants.
We generally used to split our stay in three parts, SE for upland, mideast for ducks/geese, then back SE to hopefully get the migrating birds. Next year we'll go directly up mid-east and then come back to the southeast when the birds should be thick. We are taking a bigger chance on a freeze-up by staying until the end of Oct, but I think it's worth it to have an assurance that the birds will probably be there.
I have three friends who have flown up for the last week in October (SE) for the past 5 years and had their best week this year, ever. Speaking of the ease of which they were able to get their limits. All through by 8:30 each morning. They have been frozen out a couple of times, though.
Good luck in your choice.