Hmmm, it looks kind of like the first number is an estimate of total read time since a user has joined a forum. You joined in August of 2018 and I joined in January of 2019, which seems to partly explain the difference in the first number.
Possibly, but I am not sure it can tell if you are actually reading the page, or just have it open in the browser window and you are doing something else.
Personally, I tend to open all new/unread posts in the morning, then read them whenever I happen to have time.