Edit in JSFiddle

//http://www.jermywells.com

//localStorage.clear();    
if (localStorage === 'undefined') throw 'localStorage is not supported by your browser';
var myElem = document.getElementById('myDiv');

if (!localStorage.PostCivBlogVar) {
    localStorage.PostCivBlogVar = getNeverVisitedMsg();
    myElem.innerHTML = localStorage.PostCivBlogVar;
} else {
    var newHtml = getPriorVisitMsg(localStorage.PostCivBlogVar);
    localStorage.PostCivBlogVar = newHtml;
    myElem.innerHTML = localStorage.PostCivBlogVar;
}

function getNeverVisitedMsg(){
    return '<div class="light">This was your first time here. <br /> It\'s ' + String(new Date()) + '</div>';
}

function getPriorVisitMsg(storedVar){
    return storedVar + '<div class="dark">You\'ve been here before.<br />&nbsp;It\'s ' + String(new Date()) + '</div>';    
}

<div id="myDiv"></div>

.light {
    color:white;
    background-color:#00e700;
    border:1px solid orange;
}
.dark {
    color:white;
    background-color:green;
    border:1px solid gray;
}