Yes, they can tell the time but there are better ways of knowing the time nowadays. Especially if you care about accuracy, a smartwatch connected to a smartphone connected to an atomic clock is more accurate than your Rolex.
So what's the point of jewelry? Fashion, and signaling your wealth mostly.
It gives me an ambient sense of the time because I end up glancing at it randomly. I lose track of how far along I am in the hour if I forget my watch.