A Time Ring was used by Harmonious 14 Zink to travel through time "righting wrongs" wherever he and his wife went.
This Time Ring was used during and after the events on Erratoon by Zink and Zara to aid in her search for the Key to Time. (AUDIO: The Prisoner's Dilemma)
After taking the segment of the Key to Time on Mars, Zara took Zink's Time Ring from him and used it to travel to Safeplace and to Isskar's ship on her own to continue her quest. (AUDIO: The Judgement of Isskar)
She used it again when she was a passenger on the Eschaton and during the conflict between the White Guardian and the Black Guardian on Chaos. (AUDIO: The Chaos Pool)