You're right, Cheez-It is on the same level as Gator and Holiday now, not a tier by itself. Dukes Mayo is below those three (along with the Sun and Pinstripe in tier 2). Didn't realize the Orlando bowl had dropped a tier starting in 2021.
https://www.wralsportsfan.com/giglio-projecting-the-revamped-acc-bowl-lineup/20001530/
As far as how long the current contracts run, I think they are all through 2025, according to this excerpt from the Gasparilla Bowl website:
The ACC has reached agreements through 2025 with the Belk Bowl, Camping World Bowl (now the Cheez-It Bowl), Hyundai Sun Bowl, Military Bowl presented by Northrop Grumman, New Era Pinstripe Bowl, San Diego Credit Union Holiday Bowl, TaxSlayer Gator Bowl and the new game in Boston, which will be named later this fall. The league will also send a team to either the Bad Boy Mowers Gasparilla Bowl, Birmingham Bowl or SERVPRO First Responder Bowl on an annual basis.