Saskatchewan get a lot of specks and in most areas has a daily limit of 5, so the opportunity is good. They are first to move south but they often stage in areas with big bodies of water or on the river. If your planning for early-mid sept best to go further north, in central sask they start showing up in numbers around the mid to late sept and can hang around well into october but any cool weather and they are moving(just like snows). Best advice is contact outfitters in different areas of interest and ask them if and when they see the majority of specks on average..like cyrus said weather as well as crops and water play a big part on their fly patterns and length of staging. You don't need an outfitter to hunt waterfowl here but if never been in the area it isn't a bad idea, due to area familarity and land access. Bonus is they often can be found with a mixed bag of geese (canada's-lesser and greaters, snows/blues/ross) and of course mallards. All species have liberal daily bag limits up here.
Sask. Oufitters Assoc website:
www.soa.ca
I'd check the Eston, SwiftCurrent or Deifenbaker lake areas, they have always held large numbers of specs. Although they can be found almost anywhere up here. Quill Lakes area has lots of Snows, but both honkers and specs can be found frequenting this goose hunting hotbed in decent numbers as well and it really is sight to behold to see 100's of thousand of wings flapping...get yourself a guide if you plan to hunt here as access can be very tough.
Best of Luck