The attribute dispatch.time_format is used when you specify the earliest (Start time) and latest (Finish time) of the saved search in string formatted dates. If it's relative ( e.g. -1d@d ) or epoch, then this property is not useful. If you want to specify the earliest as absolute date e.g. earliest=2017-02-06 11:00 PM , then you should set dispatch.time_format=%Y-%m-%d %H:%M %p. If your absolute date format is same as it's default value, then no need to specify that.
dispatch.time_format = <time format str>
* Defines the time format that Splunk uses to specify the earliest and latest
* Defaults to %FT%T.%Q%:z