There are a few trainers in Kanto whose cooldown to be re-challenged is longer than 7 days, namely:
Cerulean Gym
Route 16
Some in Route 8 (Stan, Aidan, Ricardo, Miranda, Megan, Leslie, Paige, Eli, Anne and Glenn, others are fine)
Pokemon Tower top floor (only the rockets, the trainers in the other floors are fine).
I'm sure of this as I've re-challenged them on Thursday last week and today, 8 days later, they're still not re-challengeable. I thought it was odd but possibly intentional, but when I asked about it on discord nobody knew about it and I was advised to report it here.