RADIUS Attribute - Event Timestamp
As per RFC 2869
This attribute is included in an Accounting-Request packet to record the time that this event occurred on the NAS, in seconds since January 1, 1970 00:00 UTC. A summary of the Event-Timestamp attribute format is shown below. The fields are transmitted from left to right.
Type (IETF Number) = 55 Event-Timestamp
Length = 6
Value = The Value field is four octets encoding an unsigned integer with the number of seconds since January 1, 1970 00:00 UTC.