Does wordpress run ‘crontab’ for scheduled cron jobs?
Answer is no. According to Codex document, scheduled tasks are executed by visitors. It means that if visitors are not accessing your blog, it won’t be executed. However, it won’t be matter for public blogs or websites due to search engine robots, which are working hearty to crawl the website.
Schedules a hook which will be executed by the WordPress actions core on a specific interval, specified by you. The action will trigger when someone visits your WordPress site, if the scheduled time has passed. See the Plugin API for a list of hooks.