Your host has disabled set_time_limit, which is used to prevent the mailer queue parse from timing out too early. You'll need to contact your host. I've no experience with one.com, sorry. I typically recommend places like siteground for Joomla installs.

Most hosts set max_execution_time to 20 - 30, which may be too little time depending on how many emails need to process. CBSubs Mailer will set this to 60. Your value of 50 is probably fine. Regardless it's just a warning and shouldn't stop the execution of the mailer and the "Could not instantiate mail function" error suggests it's making it all the way to the process of actually sending the emails which is then failing when attempting to use the mailer API. I've no idea why this impacts only CBSubs Mailer as it's the same API used to send every email in CB. You'll need to have your host check their mailer logs to see if they're rejecting the email for whatever reason as we're just calling PHP mail function.