Plugin execution on recurring schedule

I’ve written a plugin that automatically creates a post and adds an image, some tags, and a category to the post. I’m almost done, but I’ve hit a major snag.

I need this plugin to automatically do this post creation on a defined schedule. I have an admin panel where the user can specify the schedule — either daily or weekly. However, I can’t figure out how to make the plugin actually execute on a recurring/defined schedule.

For example, how can I have it call it’s function to create the post, add a specified image, and publish it, say every morning at 6:00am?

Would I need to do this from the server, perhaps a cron job that executes the PHP script on the schedule?