Use custom method for FriendlyId (Example)

post.rb

class Post < ActiveRecord::Base
  # for SO: http://stackoverflow.com/questions/10481389/friendly-id-with-two-parameters
  # EXAMPLE ASSUMES YOU ARE USING FRIENDLYID 4.X
  # AND THAT YOU HAVE A SLUG:STRING COLUMN ON THE MODEL
  # ...
  extend FriendlyId
  friendly_id :generate_custom_slug, :use => :slugged

  # ...

  # If the object is a new record, created_at and updated_at are not
  # populated at the time of generating the slug, so default to Time.now
  
  def generate_custom_slug
    "#{:created_at || Time.now} #{:title}"
  end

  # you will need to run strftime and extract the required fields to get the proper date format

end