I usually write for about 5-10 minutes in the evening to reflect on my day. My model is the emperor Marcus Aurelius and how he used his journal
I usually journal about 10 -15 minutes in the morning. Trying to become aware of my current mood and to point out to myself what I can be grateful for. Then I make a list of things I want to accomplish today. Usually this lifts me up and I am ready for the day ahead.
Varies greatly. Sometimes 5 minutes. Sometimes 5 hours. Sometimes jotting down wisdoms I want to remember. Sometimes I end up writing a lesson or an article or what becomes ideas for a book.