Pace Jacobi, Kant was directing our attention specifically to that which we could not perceive, and setting up a system for thinking about it, so that we wouldn't forget that we couldn't perceive it. It's a feature, not a bug. If you ever forget that you don't really understand, the time will have you.
No one seems to have made this argument, which is puzzling.
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Reading Peirce. An offhand mention: time as identical with inner experience, and space as identical with external experience. I don't know that the association has ever occurred to me as identity. But perhaps that's just another one of the thoughts out there that's well-known and new to me. Every thought has its time.