cesium writer: how to draw a satellite orbit

hey there.
I`m trying to draw a satellite orbit with cesium and cesium writer. I have my own orbital propagator that gives me time tagged points, but I'm having some trouble generating the czml code with cesium writers.

First thing is: the epoch property of the position element, how do I set it?
In the path section, from what I have understood from samples, I have to use lead time and trail time to show a single orbit, but I can`t quite understand how. Are those parameters compulsory?

Is there any samples that can help me doing that? I`m using java.

Thank you for your help.