There is a special property to map custom event attributes - DataTagFields.
Let's say your TimeEntry class looks like this:
public class TimeEntry {
public DateTime Start {get; set;}
public DateTime End {get; set; }
public string Text {get; set;}
public string Id {get; set;}
public string Color {get; set;}
public string Details {get; set;}
}
You will want to map Start, End, Text, and Id using DataStartField, DataEndField, DataTextField, and DataValueField.
Any other properties can be mapped using DataTagFields:
DataTagFields="Color, Details"
These fields can be accessed using e.Tag["Color"] and e.Tag["Details"] in the BeforeEventRender event handler.
See also Custom event rendering topic in the Calendar documentation (it works the same way for the Month control).