To use this code from an href you can create a link as follows:
<a href="#" onclick="SI_API.showPopup();">my live chat link</a>
In your app settings, go to the targeting tab and set the following:
Action: Show Popup on Match
After Time On Page: Ignore
This will hide the tab and the After Time on Page ignores any automatic popup. You can keep the automatic popup if you like. It works either way!