I used to work all hours of day and night, but changes in my life and physical stamina have meant that now I rarely work so long as I did-4 in the morning was a reasonable time to me, for finishing up. That isn't in my range any more.
In my 20s some of my work for children was published by Macmillan. However, I was 27 before my adult novel... was taken by DAW Books in the USA. This enabled me finally to stop doing stupid and soul-killing jobs, and start working day and night as a professional writer.