When a Job Log is copied to the Server, it is stored in a path that includes the date, e.g. 


This date represents when the job *ended*.   This is relevant when a job starts before midnight but finishes after midnight.

It is the ended time.  Specifically the “job_histories.agent_ended_time_utc”.  (timestamp captured from the agent systems clock)

Note:  The conversion of java milliseconds to a date happens on the server, so the date reflects the time zone offset of the server when the agent and server are in different time zones.