Clock-Person

The Clock people were a race who lived in the Time Vortex.

Biology
The Clock people granted individuals the ability to alter their pasts by correcting mistakes. People who accepted had their timelines erased, since it unravelled their personal history. This allowed the Clock people to take their physical place. The Clock people developed clock-like faces and had clockwork replacing their internal organs. Once the transformation/possession was complete, they could also turn back time in their immediate vicinity by two minutes, allowing them to erase moments such as being shot, but turning back even this much time caused them to expend a great deal of energy. (PROSE: Anachrophobia)

History
When Father and Mother of the Shadow Spire petitioned the loa to show them the survivors of Faction Paradox after the fall of the Eleven-Day Empire, they saw Mathara's fleet invading a sheath echo of the Homeworld. (PROSE: The Story So Far...) Following the Eighth Doctor's destruction of that Gallifrey using the Edifice, (PROSE: The Ancestor Cell) Mathara's fleet fell from the Spiral. Those cultists' souls transformed into ticking gearwork viruses that turned their human hosts into empty clock faces. (PROSE: The Story So Far...)

The Clock people evacuated the Time Vortex because of the Council of Eight. They were dependent on the breach in the Time Vortex created by Paterson's experiments, which served as their lifeline. The Eighth Doctor was able to defeat the first wave of Clock people when he released mustard gas in the base, as the gas had spread to a fatal level before the clock-faced people became aware of it to erase its release, but one of the creatures escaped the attack when it was taken to Station One and infected everyone present. Although the creatures were able to infect the Doctor, he used that infection to seal the breach by possessing his past self and setting the system up so that the breach would only collapse after the Doctor and his companions had arrived at Station One, thus ensuring that he didn't actually change history and thus make himself vulnerable to infection.

Once the creatures were defeated, it was revealed that the Doctor had been manipulated by Sabbath into a situation where he would perceive the creatures as a threat rather than refugees. (PROSE: Anachrophobia)

Behind the scenes

 * Author Jonathan Morris intended the clock-faced men to be Faction Paradox after the events of The Ancestor Cell. This was ultimately confirmed in The Story So Far... in The Book of the Peace Dossier.