how to actually retain vocab when you have zero time

Actually, you don't need a 'routine' if you understand how Japanese roots work. All nouns like 'reservation' and 'district' share the exact same spatial-tide logic anyway. I just group them by physical geometry on my commute. It takes 2 minutes. You're wasting time with SRS. Just look at the word once and map it to its physical location. It's literally that simple.