How to Determine Lead and Trail Time in CZML File

Hi, I am trying to visualize the orbit of the satellites with different position values from the simple.czml file provided in CZML Sandcastle example. However, I don’t know how to determine the lead time and trail time values for my position values and multiple lines for the orbit are displayed without those values. Can someone please help me to calculate those values or explain how the values in simple.czml file are calculated? Thank you!