From version 1.4.0, the importing of all the TLDs available to your eNom account is automated and occurs at a time according the settings set in Setup->Addon Modules->Configuration. The key settings can also be set from the 'Quick Actions' page.
If eNom TLDs have not previously been downloaded, e.g. the module is being installed for the first time or it has been Deactivated/Reactivated, then all eNom TLDs available to your account will be downloaded when the WHMCS Cron runs next irrespective of the time set in 'Run auto updates at'.
After that, future downloads will be made according the time in 'Run auto updates at', the frequency in 'Download eNom TLDs' and the day in 'Download eNom TLDs on'.