I would like to know the time period during which the customers have the highest number of visits.
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You can do this with the Discourse Data Explorer plugin.
I’m not quite clear what query you are looking for, though. You want a period of some hours that has the highest traffic? Maybe the existing graphs on the admin panel can help?
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The data explorer is the plugin for querying your site’s data if the dashboard reports don’t meet your needs. 
Unfortunately in this case, the time of visit isn’t recorded in the database so I don’t believe it’s possible to report on the busiest times of the day, if that’s what you’re intending.
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In that case then a tool that consumes the nginx logs is what’s needed. They are in shared/logs/var-log/nginx if I can type and remember correctly, which is rather unlikely, but that’s the idea.
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