Can someone explain the Active Now & time stamp?

When you swipe left on your phone and it brings up the people you communicate with the most, it'll either have the active now green dot, how long it's been since they were last active, or the little mobile icon. I just want to know exactly how accurate that is. I'm trying to find out if I'm being ignored by people or if it's just not accurate. I've seen forums where people say it's not accurate but I wasn't sure if Facebook has since fixed it. Any thoughts? Thanks!