Free year ATV+ with student AM subscription?

I am currently on a student subscription to Apple Music for $4.99 per month with complementary Apple TV+ included; that offer should expire later this year and I won't be renewing it. (I was using AM mainly on Android, but also with iTunes for Windows plus rarely ATV+ on ATV apps for Roku & Vizio.) Meanwhile, I just bought an Apple TV 4K & was offered free ATV+ for a year.

I'm trying to figure out the best way to coordinate these so I can keep the student subscription as long as I can, but still use as much of the free year of ATV+ as possible. I know I have 90 days to redeem (the clock just started this week); the last I checked I still have the opportunity to redeem in the ATV 4K. I don't wanna wait too long just in case you try to hit me with the July 1 change to 3 months free ATV+, however. (I might also get the 1-year offer again before July as I should be getting a new iPad via my local newspaper, but that's not certain as it could be double-dipping & that iPad may not qualify.)

What will happen if I redeem the 1-year offer now? I know another answer suggested it will kick in at the next billing opportunity, but I still have those monthly thru my AM student offer where my current "free" ATV+ is from. I don't wanna redeem it too soon, but I don't wanna wait too long & lose the free year entirely or see it cut to 3 months.