It depends. Totally random.
Moderators have lives too. Sometimes three of us are on at the same time, sometimes no one is on.
It's not like this is a paid job for us.
It's not like we are assigned shifts so the moderation que is always checked.
Working from home the past two years I find myself picking up my phone and checking UG a lot more during the day then when I was in the office. Once I go back to the office I'll be on a lot less during business hours.
Conversely on the weekend and at night during the week I'm on a lot less.
I can't speak for the other mods but I know they have their times when they are more available.
Also after being on the computer for work all day the last thing I want to do is read a long ass post with no line breaks.