Hi my friend
Your IELTS result should be validate at the time of SUBMISSION of your profile, whether you are submitting a profile to SINP, OINP , MPNP ... or CIC (federal stage).
Let me give you an example:
As you said, your IELTS test is validate until May , 2017.
Lets say, you would SUBMIT your application to SINP On April 1, 2017 and, apparently your IELTS is acceptable for SINP officers.
http://www.saskatchewan.ca/residents/moving-to-saskatchewan/immigrating-to-saskatchewan/saskatchewan-immigrant-nominee-program/applicants-international-skilled-workers/international-skilled-worker-saskatchewan-express-entry/required-documents-for-saskatchewan-express-entry
Suppose, it takes 90 days to get nomination, which would be the 1st of July, 2017 and you want to SUBMIT to federal stage. Unfortunately, at that time your IELTS would be expired, and CIC will not accept it.
http://www.cic.gc.ca/english/immigrate/skilled/language-testing.asp
They will return your file and you are required to retake IELTS and send them the result.