Write in a disciplined manner, but write in a way that is natural to the individual's thought processes.
To come up with the ending to a story and then work backwards is like tying your shoe with one hand only.
I do not write by any set time schedule. I realize there are many writers who follow a daily regime where they arise at 6:00 a.m., do some sort of exercise, eat breakfast and then sit down and produce words for a three to four hour period.
I've been a writer for 42 years and, yes, it is a full time job for me. Not a hobby, but serious work.
My first novel took 12 years to complete because life got in my way.