I think he started using it when Gojo used DE for the second time, because during Gojo's first DE usage, the sure hit effect of Sukuna's DE was still active inside the domain.
It's during Gojo's second DE attempt, that Sukuna purposely deactivated his sure hit effect inside Gojo's domain, with Gojo according to this latest translation wondering why Sukuna took such a risk instead of trying to destroy his domain from the inside since he can only switch interior/exterior conditions.
So imo after the first domain clash, with Gojo recovering his CT through RCT, Sukuna probably wanted to take that opportunity to use Mahoraga's wheel to start adapting to Gojo's CT, but since he knew that with Gojo's knowledge of Mahoraga, if he saw it, he'd try to destroy it before it could adapt, he hid the wheel and made the adaptation happen in the shadow, even if he had to take unnecessary risk since as Gojo said, he could have tried to destroy his DE from the inside avoiding such a risky strategy