If I may be so bold...I strongly recommend doing whatever you can to separate handwriting from composition from editing. They are very different tasks that demand very different skills sets.
I prefer short handwriting lessons that don't require that DS8 get his own ideas down on paper (unless he chooses to do so--it's okay if he wants to, but it shouldn't be required). He writes 4 lines of careful cursive each day, all words or sentences assigned by me. DS8 doesn't have a lot of trouble with handwriting. If it were hard for him to write, less than this would probably be better. You want high-quality work and good practice, not a tired, frustrated, angry kid. It usually takes DS8 5-10 minutes to complete his handwriting.
We have a separate time to work on composition. This should probably be the longest time spent on it of the three. He can type his work if that works for him and isn't too slow to be frustrating to him (or to you!). But it's perfectly okay for him to dictate his composition to a voice recorder or to you instead. (Just refrain from editing for him. This is hard for me!) The focus here is on his thoughts, his ideas. For a 9yo, it doesn't have to be more than 15 or 20 minutes.
Finally, allow a third (short-ish) period for editing and proofreading his writing, focusing on organization, word choice, grammar, spelling, etc. This helps to combat perfectionism, too, since it allows him to worry less about getting it exactly right in the composition phase. Unless his composition is a real mess or there are grammar lessons required to explain why something must be changed, 5 or 10 minutes is probably enough editing and proofreading.
So there's a 30-minute lesson, give or take, and it will probably be pretty productive AND pretty painless for him. It works at our house, FWIW.
