There are some days I don't check in at all (and for awhile I didn't have internet access except one or two days a week), and occasional days when I end up spending an hour to an hour and a half. I do most of my shopping online, so if I am shopping online I might spend more.
I have some days where I have quite a few hours that can't be used for anything productive because of symptoms/fatigue from my health issues. I often spend that time online because it makes me feel productive to be reading and "researching".
The biggest suck for me isn't reading posts because I am an excellent speed reader, it is replying. I have a ton of ideas, but I tend to get frustrated because most of my YLF time isn't when I am mentally very sharp and the mind fuzz from my health problems tends to impede my communication skills. So, I try to pop on, read a whole bunch of posts, and then shower/do chores, ect. so I can formulate what I want to say. Then I pop back in and write for 5-10 minutes.
Most of my YLF time is the time between other tasks throughout the day.
When I was in a different situation I did what others have said and spent 15 minutes with my coffee and breakfast in the morning and then 15-30 minutes in the evening when I am unwinding.