Time stamped indices use your selected time range to create a list of
indices that match a specified timestamp pattern. This can be very
efficient for some data sets (eg, logs) For example, to match the
default logstash index pattern you might use
"logstash-"yyyy.mm.dd. The quotes around "logstash-" are
important as they instruct Kibana not to treat those letters as a
pattern.
See http://blog.stevenlevithan.com/archives/date-time-format for documentation on date formatting.