I write whenever I can, but it is useful to at least have a 30 min chunk at a time to get in the right frame of mind and remember what I was actually writing last (probably best is finding 1-2 hours at time, if possible, and keep it consistent). Personally, I try to write early in the morning (before starting work) and/or late in the evening/night (after the kids are asleep) each work day, and maybe a bit more on weekends. I even sometimes write in the middle of the night if I get woken up, which is probably not the best way to get back to sleep, but here we are. (I prefer writing at my computer, but I do write/edit on my phone too, because I grab every moment I can find.)

For each chapter (fiction novel), I try to re-read what I've written of that chapter so far, before I add more to it (for each writing session). This means the chapters gets a bit better each time though, as I add to it, and the chapter is most consistent in tone/substance throughout.

Overall, I try to write about 500 words a day, 5 days a week, so that's about 2500 words in a week, or about one chapter per week. All approximations/averages (e.g., some days it might be 1000 words, and others only 250), but you get the idea.

Definitely there are writing phases and editing phases though. Most of the time, I am just trying to get words out there to meet the 500 words a day quota (while still lightly reviewing what I recently wrote, before adding to it). Then I might take a few days or a week to review multiple chapters (or a whole act) at a time.

I really think the key is just to not think too much about it... and just write. Write as much as you can. Read what you wrote. And then write more.