A lot of things rely on GNSS for time synchronization, even if they're not moving....

These are bizarre assertions. GNSS is one way to navigate, and GNSS is one way to synchronize time-of-day. Communications networks are full of devices that don't have, or use, any GPS receivers at all. NTP, WiFi, DOCSIS, DSL, leased lines, servers, core routers, switches, desktops and laptops are all things that won't even notice that GPS was unavailable.