You can use jquery events to create your own callbacks for timelineJS

callbacks.js

$('#timeline-embed').delegate(".vco-timeline", "UPDATE", function () {
    console.log('UPDATE', this);
});

$('#timeline-embed').delegate(".vco-timeline", "LOADED", function () {
    console.log('LOADED', this);
});

$('#timeline-embed').delegate(".marker", "click", function () {
     console.log('.marker', this);
});

$('#timeline-embed').delegate(".nav-next", "click", function () {
    console.log('.nav-next', this);
});

$('#timeline-embed').delegate(".nav-previous", "click", function () {
    console.log('.nav-previous', this);
});

$('#timeline-embed').delegate(".zoom-in", "click", function () {
    console.log('.zoom-in', this);
});

$('#timeline-embed').delegate(".zoom-out", "click", function () {
    console.log('.zoom-out', this);
});

$('#timeline-embed').delegate(".back-home", "click", function () {
    console.log('.back-home', this);
});