By default, Matomo (Piwik) reports are processed when you request them in the User Interface. Please see How to setup auto archiving of your reports every night? to automate the generation of Matomo reports. See also How long does the Matomo archiving process? for expected speed for high traffic websites.
If you are running Matomo (Piwik) analytics for a high traffic websites (or hundreds of them), see our guide Optimize Matomo server for speed.