It's funny how differently we all work. I can't work in dribs and drabs - I find it to hard to 'get back in' to what I was writing if I stop all the time - and I have teenagers so I get interrupted a LOT! Whenever I've tried to write like that the quality goes right down. But if I can just clear the decks for some quiet time, I can easily write 1500 words without stopping, though it's more like 700-800, then a break, then maybe 300-400 more plus some tweaking. I don't make a lot of changes but I do have to do them before I can carry on. The thought of writing a novel on my phone makes we want to weep fgs. I don't know how you do it!
One of the things that motivated me was thinking about all the time I spend writing long posts on here or another forum I spend time on. It's pretty easy to write a couple of hundred words of well thought through polemic without even blinking. I've spent lots less time on here since I got serious about working on my ms, and in particular I've avoided AIBU, which is a shocking timesink!
I'm not really a morning person, but increasingly I've found myself getting up earlier than the slumbering teens on the weekend, which can give me some excellent quality time for writing or researching - something like 8 til 10 can be magically quiet, or even later. In the week, I tend to write in the late afternoon between about 4 and 7. Dinner's been getting later and later. Everyone in the house knows the book's been going well when 'mum's had another dinner fail'. It must be totally different if your kids are small though. 15 years ago, I was writing romances and used to do it when the eldest was at nursery and #2 having his nap. When he outgrew his nap, I used to put him in a playpen 
and sit in the cupboard under the stairs with my laptop - until the day he learned how to climb out of the playpen, which is about the time my writing career stalled.
I'm writing crime now, which I guess is 20 years of marriage for you. 