app-models-foo.rb

class Foo < ActiveRecord::Base
  extend TimeScopes
  # ...
end

lib-time_scopes.rb

module TimeScopes
  def today(now = Time.current)
    where('created_at BETWEEN ? AND ?', now.at_beginning_of_day, now.at_end_of_day)
  end

  def yesterday(now = Time.current)
    today(now - 1.day)
  end

  # ...
end

original.rb

{
  :today => where(['created_at > ? and created_at < ?', Time.current.at_begi…
  :yesterday => where(['created_at…
}.each {|name, time_period|
   Foo.in_time_period.count # magic?
   Bar.in_time_period.count # same magic!
}