Google limits the maximum duration of a script to 6 minutes. That means you can find between 300 and 500 email addresses maximum at one time, then re-launch it manually.

For the same reason, it isn't possible to select a list of more than 500 domains or company names for the bulk Domain Search on the Google Sheets Add-on. Even below this number, the script could potentially time out before all the domains have been searched (especially when requesting more than 10 emails per domain).

For big volumes, we recommend using our Bulk Email Finder and Bulk Domain Search on Hunter's website.

Here's also a dedicated video tutorial for the Bulk Email Finder functionality, and another here for the Bulk Domain Search functionality.