For the other site (Buy Graduation Balloons, Customised & Personalised Balloons Singapore – The Balloon Studio) you have a lot of additional trackPageView events added directly to the page source. Because of that, each page view is counted a few times which affects the time on page metric. Keep in mind that Piwik PRO does not work out of the box with Matomo code installed. Here is a guide on how to set it up.