Everyone has their own pattern, limits and process. I consider my process to be pretty slow to be honest, but I’m content with it because it allows me sufficient study time as well as allowing myself free time outside of study. Which is super important, especially when working full time.
As you are starting with N5 grammar, it probably feels like it is taking forever because you’ll be subconsciously establishing your personal learning habits. It can take a lot out of you without realising.
Please don’t be too hard on yourself. I have days where I feel like I should be a lot further on than I actually am. I’m sure everyone does. But we should never let it get the better of us.
If you feel like you are sufficiently challenging youself, and you’re managing to retain the information you’re learning, then you’re doing great. If you genuinely feel like you could push a little harder, then by all means do so!
We’re behind you either way