ruby - Rails not including timestamps even though I specifically ask for them

I am currently having a problem with RoR. I need the fields created_at and updated_at in in my tables for further use. However rails doesn't seem to add them even though I ask rails to. These are my models:

Picture.rb
class Picture < ActiveRecord::Base
belongs_to :category
has_many :comments, dependent: :destroy
mount_uploader :photo, PhotoUploader
validates_presence_of :photo
end
Category.rb
class Category < ActiveRecord::Base
has_many :pictures, dependent: :destroy
validates :name, presence: true, uniqueness: { case_sensitive: false }
end
Comment.rb
class Comment < ActiveRecord::Base
belongs_to :user
belongs_to :picture
validates :text, presence: true
end

These are my migrations:

class CreateCategories < ActiveRecord::Migration
def change
create_table :categories do |t|
t.string :name
t.timestamps
end
end
end
class CreatePictures < ActiveRecord::Migration
def change
create_table :pictures do |t|
t.string :description
t.references :category, index: true
t.timestamps
end
add_foreign_key :pictures, :categories
end
end
class AddPhotoToPictures < ActiveRecord::Migration
def change
add_column :pictures, :photo, :string
end
end
class CreateComments < ActiveRecord::Migration
def change
create_table :comments do |t|
t.string :text
t.references :user, index: true
t.references :picture, index: true
t.timestamps
end
add_foreign_key :comments, :users
add_foreign_key :comments, :pictures
end
end
class AddTimeStampsToPicture < ActiveRecord::Migration
def change_table
change_table :pictures do |t|
t.timestamps
end
end

As you can see I am trying to add the 2 columns. When I try seeing the created_at field it will say "undefined method created_at'" . I am checking in rails c to see if the fields are there but no, the fields do not exist. I am using PG gem . Also I am using carrierwave gem to upload the pictures. Why would rails not include these 2 columns ? Here is a link to the project itself.

As coorasse suggested I took a look at the schema.

create_table "pictures", force: :cascade do |t|
t.string "description"
t.integer "category_id"
t.string "photo_file_name"
t.string "photo_content_type"
t.integer "photo_file_size"
t.datetime "photo_updated_at"
t.string "photo"
end

It seems it didn't update herself. Why?