The Clock people were a race who lived in the time vortex.
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. 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)
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, 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 setting the system up so that the breach would only collapse after the Doctor and his companions had arrived at Station One.
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)