通过覆盖下面两个方法可以实现，虽然使用场景不多，但也是个 Feature

class User < ActiveRecord::Base

  # 非必需，但是 Rails 源码是 Private 的，尽量保持一致  
  private

  def timestamp_attributes_for_create
    ["created_at", "created_on"]
  end

  def timestamp_attributes_for_update
    ["updated_at", "updated_on"]
  end
end

Rails 源码在这 https://github.com/rails/rails/blob/master/activerecord/lib/active_record/timestamp.rb#L69-L75

希望我不是最后一个知道的。