I don’t think I would use cron jobs for this at all. If I was writing code for it I would probably have a check on the page that just says if the user is part of x group and date is greater than the event start date then render the page, otherwise return a message saying it’s too early, check back later.
Either that or just setup the page/post so it’s scheduled to publish on the date of the event. If the content should only be available to users in a certain group use a membership plugin with the ability to restrict content to members of that group.
When you schedule a post it will get picked up by the WordPress cron, this can be setup in a couple of different ways.