Good point regarding time. Quartz watches need a battery, but many also need a regular update from a time source like WWV. Many watches are sold as atomic time pieces, but really they are mediocre timepieces with a small radio receiver designed to give them a daily time tweak to give the illusion of a precision timepiece. If the GPS signal is shut down, who's to say that WWV doesn't also get turned off. As time errors increase, accuracy of a celestial fix is reduced.