sitecore index rebuild scheduling
How to rebuild coveo sitecore index programmatically from a scheduled job?
Programmatically rebuilding the Coveo for Sitecore indexes is already documented (see Refreshing or Rebuilding a Search Index Programmatically).
For the "scheduled job" part, I know that Sitecore has some scheduling features. You should check on Google for "Sitecore scheduling" and "Sitecore scheduled tasks".