This is a small change.
http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/PatternLayout.html conversion character d-
"For better results it is recommended to use the log4j date formatters. These can be specified using one of the strings "ABSOLUTE", "DATE" and "ISO8601" for specifying AbsoluteTimeDateFormat, DateTimeDateFormat and respectively ISO8601DateFormat. For example, %d
So we should switch our date, as we could get better performance out of the logging.