Hmm I don't get as much done as I hoped to, and certainly no big projects like writing a book. Two school aged kids, and we're in France so the school day is long - 0830 to 1645 every day. I'm working very part-time within school hours now.
There are certain things I do that take up more time than they would if I cut some corners. So I cook from scratch, always. I shop at the market for fruit and veg at least 2-3 times a week, plus one big shop by car. Pretty much all the housework gets done during the day. I am an avid Kondo-er and have decluttered everywhere. I used to do a major volunteer role, which took up a lot of time but have cut back on that since I started working. I help out regularly at the youngest's school - reading, accompanying them to trips and sports things. I cover all the sick kid days, random school strike days, school meetings, etc so that DH doesn't have to. I do all our admin - tax returns, medical stuff - normal life in France is very admin-heavy, not least thanks to Brexit and needing to get residence cards / driving licences / nationality applications on the go (humph! - a full time job in itself). I do all our decorating and lots of DIY - we live in an old apartment, there's always something that needs repairing or fixing up. I also scour FB for good quality second hand furniture and white goods when we need them - much cheaper but a lot more time-consuming than just buying new. Oh and yes, organising holidays, activities (again a time-consuming thing here as nothing happens through the schools, they all have to be done through various associations - each of which involves a different sign-up and medical process). I also organise all our family travel - we have family back in the UK that we try to see at least a couple of times a year, which gets very complicated between holidays and different timetables. So I spend a lot of time negotiating with my parents, DH parents, both our sisters and their families to organise trips at Christmas and during the summer - as well as try and get some time just for us! So I get a shitload done, and take the pressure of DH who works long hours in a demanding job, but it easily fills the time alloted to it.
However, the real point of my post is that over the 10+ yrs of being a SAHM and working pt is that if you want to achieve something out of the ordinary - writing a book, creating a successful blog, major decorating project, learning a language, commit to a gym or sports routine, whatever - you need to treat it as if it was work. You need to separate out the time that you are going to spend on it, schedule it into your diary and enforce it in someway (this is the hard bit when it's not a work situation, there's no boss standing over you). It won't just happen as it will always be pushed to the side by the more immediate / pleasant tasks that need done. No-one's really going to notice if you haven't learned to speak Mandarin or haven't done Couch25k... but they will notice if the dog isn't walked, they're eating frozen pizza and oven chips for tea or they've got no clean pants or they've missed their tetanus booster vaccination date etc etc.
So yeah, if you want to achieve something beyond the daily grind, get it in your diary and commit to it. It's the only way.