I would say deep thinking work, I average around 3-4 hours, but range between 0-8 hours. Like if I really feel in zone, it's easy to go hard, but if I didn't sleep well, or had too much caffeine, or didn't eat enough, it's just joever. I think months of grinding is possible with the right motivation, but I find that trying to force that motivation is pretty hard; I think that's often more environment-based, rather than solely individual effort (ala being in a class of very motivated individuals)
The important part for me is trying to start every day (or whatever your schedule is), because it can be hard to know how well I'll concentrate until I try for 30 minutes or so. And consistency over a long period of time is key.
edit: oh, fwiw, specifically for Chinese, I have been building this recently... although it's not done yet. https://hanzi.bpev.me/