columnBubble - get Date of Column

Hello,
im evaluating DayPilot Pro for my Project.

I want to Display some special Infos in a columnBubble and there i need to have the Date of specified column. I can only get the ID of the resource. Im Using the DaysResources Calendar similar to this
https://javascript.daypilot.org/demo/calendar/daysresources.html

Here is my code:
dp.columnBubble = new DayPilot.Bubble({
cssOnly: true,
cssClassPrefix: "bubble_default",
onLoad: function(args) {
var c = args.source;
args.async = true; // notify manually using .loaded()

// simulating slow server-side load
setTimeout(function() {
args.html = "testing bubble for: <br>" + c.id + " date: " c.start; // resource id in resources view
args.loaded();
}, 500);
}
});

c.start is undefined, it doesnt work with c.start() and also c.name is undefined...

Maybe im totally wrong?

Thanks for your help