Regeneration cycle (The Christmas Invasion)

The regeneration cycle was the time during which the process of regeneration occured. The newly regenerated Tenth Doctor credited the manifestation of a new hand to replace the one severed by Fadros Pallujikaa to having still been within the first fifteen hours of his regeneration cycle, which provided him with "just enough" residual cellular energy to regrow his severed limb. (TV: The Christmas Invasion)