I spend the most time on LJ during the evening, but I do usually check it in the morning at work to catch up on what has been posted since last night.

A slow day at work means I might be logged in frequently, but my quality LJ time is in the evening.

I usually log in at random times during the weekend, but always Sunday evening (although lately TV is getting in the way of my Sunday night LJ time).

As far as download stats go, Monday and Thursday evenings are very popular.