Yes, it takes a short time to make a post, but first the person would be browsing through the site, find the topic/image/whatever to be commented on, think about what to say, then make the post, all of which takes a lot more than 30 seconds, especially since people don't just use 30 seconds of internet a day to make a post.
I understand taking the laptop into the kitchen, but I don't know why other people wouldn't do it.
And people do spend a lot of time on the internet without doing anything else. I'm not saying it's smart, I'm not saying they shouldn't do it while cooking, I'm just saying people do spend a lot of time on the internet without doing anything else, such as cooking.
You didn't say anything about 14 hours. Your example is with 9 hours plus 30 minutes of break time <_<