Are you thinking the segment method just isn't worth it?
I'd like to use the ACA maps for my first bike tour. Maybe I could find a loop that keeps me close to home but uses ACA routes.
Section hiking is a bigger deal with long-distance hiking because there's basically three long distance trails, and completing any of them in one season can be difficult due to the length of time it takes, and the weather.
"Section biking" has never really become a thing, probably because as cyclotourists we are not limited to a handful of very defined route options. Also, "I biked the Northern Tier" doesn't have the same ring or importance as "I've completed the AT" or even "I biked from coast to coast." Granted, biking the complete NT does
mean you've biked coast-to-coast, but more people care about the coast-to-coast
part, not what particular line on a map you followed.
I'd encourage you to use your nine days at a time to do a couple local tours first. You might not even know if you like to tour or not. And trying to break down a long-distance tour in seven (or less) day chunks with the headaches of figuring out how to get to and from each segment may suck all the joy out of the actual tour.
As for local and ACA routing, besides Route 66 and North Lakes Loop, the Northern Tier comes pretty close to Chicago. You may be able to take a train out to a nearby point, then ride westbound. The NT through Iowa and southeast MN hugs the Misssissippi Valley, which is quite scenic. And you could make it to a place like La Crosse or St Paul where you could hop on Amtrak back to Union Station in Chicago.