I have a job that makes me to be too busy and whenever I close from work I feel so tired, and I don't even have the energy to login my forum account. The only time I'm free is on weekends and my family is large, if even you want to do something else you may get distracted.
I want to know how you use the forum. Can you engage in forum discussion when you are in the midst of people that your attention can be called at anytime. Or you use the forum when you are free alone, like in the midnight when every where is quiet.
Because I know some forum discussion needs critical thinking and if you are distracted it can decline the quality of your discussion.
As you said, I use the forum more often when I have free time, and it is true that it is more often at night or in the middle of the night, because it makes me feel calm without any disturbance, especially the calmness of the sound is much better than during the day. But I think it all depends on each individual, because someone may feel calm and not disturbed in the morning or afternoon. So for yourself, I think you know better when the right time for you to use the forum, and it should not interfere with your work time either, because I think work requires professionalism.