In the dayPilot Calendar javascript open source version, in order to get a tooltip I did patch the code like this
the patched file is : js/daypilot/src/daypilot-calendar.src.js
look in the source code after the following function:
this._drawEvent = function(e) {
then find the place where the inner Div is created :
var inner = document.createElement("div");
inner.setAttribute("unselectable", "on");
inner.className = calendar._prefixCssClass("_event_inner");
inner.innerHTML = e.client.html();
// Robert - 11 May 2016 - event tool tip
if ((e.data.start instanceof DayPilot.Date) && (e.data.end instanceof DayPilot.Date)) {
// dont use the toolTip content which might be not pure ASCII
inner.title = e.data.start.toHourString() + ' - ' + e.data.end.toHourString();
}