Mix it up a little. What I've found when writing is that if I'm too focused on the plot or thinking about some other scene while writing this one I'll not write much. I once took a day off studies to finish one of my stories, thinking I'll finish the last 5 chapters today and completed absolutely nothing. The whole day, I was simply staring at my screen, thinking I have to finish this, then I have to start this scene on the next chapter. Stuff like that. What helped was taking a break. Not from writing (even though sometimes it does help) but from my story. I ended up writing a one shot for my otp. And after that when I started on my story again, I wrote 10k words. The chapters weren't complete, but I had accomplished more than I would have stuck to that one story. Also, editing your previous chapters is a good way to refresh the plot in your mind and you might get a better sense of where you want to take the story next.
I've written that amount in an hour before. I've also written that amount over the course of a month. If it flows, it'll flow. If not, let it go.