A setLifeTime() method would be very-very handful to change the lifetime without initialize a new cache object. At the moment we must have as much cache object as much lifetime we want use instead of using one cache object.

if(!$cache->start('mypage')) {
        echo 'This is cached with init lifetime ('.time().') ';
        $cache->end(); 
}

$cache->setLifeTime( 3 );

if(!$cache->start('mypage2')) {
        echo 'This is cached with 3 seconds lifetime ('.time().') ';
        $cache->end();
}