I do this in the morning right after my routine. I sum up the lesson from the past day, then set a goal for the new one.
In the evening before bed. I mainly focus on a short summary of the day and write my overall feeling of det day. I can emotionally be somewhat unstable, so i like to check in with myself and try and keep track of what could possibly affect my mood.
I always set 2 times a day of writing journal — in the morning before working and the another one before sleeping. In the morning, I plan for only 2 to 3 minutes writing about how I want to be, feel and do during the day. While in the evening journal is more on reflecting 2-3 important things impacted my feeling. This is when I can release my tension at the same time of rethinking carefully on the solution to improve self. I know this sound too much but it helps me become a better aware of myself and manage the situation easily
To be honest, I never manage to set aside a precise time… sometimes I write a bit just before dinner, sometimes just before bed, sometimes I skip a day, but then write for two days the next day! I find setting a precise time in the evening difficult, so just let myself do it whenever I manage (as long as I get to do it at all!).