From the air canada web site:
https://www.aircanada.com/wallet/ser...milyPageDetail
Upgrades:
Complimentary upgrades are offered with the Latitude fare option only and are subject to availability of the Executive Class fare (J booking class), wherever offered;
Complimentary upgrades can only be requested and confirmed online between 24 hours and one (1) hour prior to the original flight departure time and cannot be processed at the airport;
Complimentary upgrades do not grant access to Air Canada Maple Leaf Lounges, nor to any airport lounges;
Air Canada Top Tier upgrade certificates are also permitted, as per the terms and conditions on the certificate.
If they are not allowing the 24h complimentary upgrade even if J=1, then they have changed this term of the pass, without making this change in the list of terms, dealing with complimentary upgrade.