CIS players , for most of the country, have 7 years to complete 5 years max of playing football.( no other sport has this restriction) Most don't make a competitive roster at age 18 . The old rule was based on starting your post high school education.
So whether you sit for a couple years on the practice roster, do a victory lap, play junior football or go to the CEGEP in Quebec, your draft eligibility will start 3 yrs after starting to play in the CIS. Some players may only play CIS for 3 years. Eg at Laval, not many are starters their first year Most players / coaches will try and plan their schooling etc in order to maximize their eligibility.
In the Q, they finish high school at grade 11 then continue onto CEGEP. So in Quebec, they have 8 yrs after high school to complete max 5 yrs playing in the CIS. Usually, one takes 2 yrs of CEGEP before continuing onto university. Many will stay an extra year for development .... Some even 4. Of course the extra years cut into their eligibility years.

Of course the CIS is looking at changing their eligibility rules to a straight complete a max 5 years of playing before age 24 .... Problem is a some provinces base their school age on the school year ( sept) rather than the calendar year.... Which makes the rule discriminatory for those whose birthdays are October to dec. ....... Sorry to rant and confuse the matter further.

For both the CIS and the NCAA new rules, it will be better for the teams. At least
i) the players, if drafted can join the team for training camp that year. The CIS players can be sent back for their last year of eligibility. I believe if they have been drafted, there is a 2 year limit where the player is still "property" of the team ..... Or the team that drafted them has first dibs for 2 yrs.
ii) the NCAA player can show up for the e camp and training camp without being penalized.