[рони]

smart-create,

var limit = 2 * 24 * 3600 * 1000; // 2 суток
var localStorageInitTime = localStorage.getItem('localStorageInitTime');
if (localStorageInitTime === null) {
    localStorage.setItem('localStorageInitTime', +new Date());
} else if(+new Date() - localStorageInitTime > limit){
    localStorage.clear();// localStorage.removeItem('result') 
    localStorage.setItem('localStorageInitTime', +new Date());
};
function str_rand() {
    var result = '', words = '1234567890qwertyuioplkjhgfdsazxcvbnm';
    for( var i = 0; i < 6; ++i ) {
        result += words.substr( Math.floor( Math.random() * words.length ), 1);
    }
    return result;
}
var result = localStorage.getItem('result') || str_rand();
localStorage.setItem('result', result );
alert(result);