In a sense, a POW blockchain such as bitcoin can convey global time/global clock if all participants understand the average block propagation is 10 "minutes"? Sometimes longer, sometimes shorter but converges to 10 minutes in aggregate.

Over great distances this breaks down given limits on the speeds of transmition (speed of light), however, if transmission was instantaneous (quantum entanglement?), that would solve the dilemma of what does "now" mean light-years away given our relativistic idea of time between here and there.