Generally one runs defined cron jobs on a schedule set in advance. This allows you to queue up arbitrary methods to fire at arbitrary times, generally "a short while after this HTTP request has been dealt with."

This is an extraordinarily common pattern in web applications. My Rails apps do it hundreds of thousands of times per day, often to avoid hitting an external API during a request/response cycle. (I use Delayed::Job. This would not be my #1 recommendation for this pattern in 2014. Take a look at Sidekiq, Resque, or this new thing instead.)