I tend to compose when I have a commission.
One of my requirements however is LOTS of sleep.
Composing is, for me, a profoundly intellectual pursuit. The emotion comes from my handling of the material. If I've dealt with it deftly, then the emotions I want to express should be there.
So when I'm fully rested is usually the time I compose most.
And like many here, I tend to work obsessively when I AM working on something, whether it be the actual creation/composition of a work, or the day-to-day tedium of cleaning up a score and preparing instrumental/orchestral parts.
I find that as I've aged, my composition rhythm seems to have slowed down a bit.
30 years ago, I was writing continuously, every single day.
Now, I find that I am more purposeful in my work, more regulated.
The last new things I wrote were the string quartet, the violin concerto, and the concerto for string quartet and orchestra.
But I've more or less worked on a single piece per year.
While that means my catalogue is relatively small, it also means I am more satisfied with what does end up at my publisher's.
Right now, other than preparing orchestral parts and cleaning up scores, I am working slowly on the opera commission. It's not a huge work, two singers, chamber orchestra, and around half an hour of music, so it's more or less equivalent to my 1st symphony as far as amount of work is concerned.
The only thing slowing down the work is that I am also writing the libretto.
I have two other pieces sort of sitting on my work table: a 2nd string quartet, and a piano concerto.
I know the former WILL get performed, and most likely many times. So that's a very exciting project.
The concerto, however, is still VERY much "in the air". The pianist involved in the commission (it's actually officially being commissioned by the conductor and orchestra) seems not to be as enthused by the project. Her attitude has sort of cooled my own enthusiasm for the project.
So chances are likely that I'll only be working on the opera for the next 9 months, and possibly getting a bit of sketching in on the string quartet. And that little/much composing is ample for me.
The opera is already going to be quite emotionally draining (the subject is VERY dark).