WpRightOnTime is a webcron service dedicated to WordPress powered sites.
It enables its users to control all scheduled events, by overriding the visitor-activated cron system, with a user defined call to wp-cron.php.
WpRightOnTime is a webservice, you can start with a free account.
To use this service you will need a valid API key from wprightontime.com.
This plugin is the interface for connecting with the service API.