_form.html.erb

<%= f.select :atime, @time_options %>

error.rb

undefined method `empty?' for nil:NilClass

model.rb

  def self.time_options
    start_of_day = Time.zone.now.beginning_of_day
    start_time = start_of_day + 9.hours
    end_time = start_of_day + 17.hours

    lunch_start = start_of_day + 13.hours
    lunch_end = start_of_day + 14.hours + 30.minutes

    times = []
    until start_time > end_time
      start_time = (start_time + 30.minutes)
      unless start_time >= lunch_start && start_time < lunch_end
        times << start_time
      end
    end
    times.map{|t| [t.strftime("%I:%M%p").downcase, t.to_s(:db)] }
  end

models_controller.rb

def new
  @time_options = Appointment.time_options
end