How does Upcase handle emailing billing reminders to users?

I’d like to start sending regular emails to my users reminding them of an upcoming charge to their card.

How does Upcase handle this? Specifically the timing aspect, sending emails a few days before the charge.

looks like it’s triggered by a rake task:

https://github.com/thoughtbot/upcase/search?utf8=✓&q=upcoming_payment_notification

it’s probably a cron job, but i don’t see anything in the repo about how that’s handled.