Where an option is exercised in favor of service and repair under Section 1793.3, such service and repair must be commenced within a reasonable time, and, unless the buyer agrees in writing to the contrary, goods conforming to the applicable express warranties shall be tendered within 30 days. Delay caused by conditions beyond the control of the retail seller or his representative shall serve to extend this 30-day requirement. Where such a delay arises, conforming goods shall be tendered as soon as possible following termination of the condition giving rise to the delay.