As other commenters have mentioned, 0 seconds doesn't mean anything. Meanwhile, those 18 visitors who spent more than 1800+ seconds on your page? Probably they

As other commenters have mentioned, 0 seconds doesn't mean anything. Meanwhile, those 18 visitors who spent more than 1800+ seconds on your page? Probably they just opened the page in a new tab and only got around to reading it a few hours (or days) later. So data at both extremes are useless. If we ignore the 0-second anomaly, it looks like we've got a nice bell curve peaking between 180-600 seconds, probably closer to 180 than to 600. That sounds about right for a 670-word article.