kibana/docs/user/reporting/report-intervals.asciidoc

[IMPORTANT]
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The interval between report requests must be longer than the time it
takes to generate the reports--otherwise, the report queue can back up. To 
avoid this, increase the time between report requests. 

By default, report generation times out if the report cannot be generated
within two minutes. If you are generating reports that contain many complex
visualizations or your machine is slow or under constant heavy load, it
might take longer than two minutes to generate a report. You can increase
the timeout by setting `xpack.reporting.queue.timeout` in `kibana.yml`.
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