The average Need Cycle for a healthy renSime is approx 28 days. A channel might have a 30 day Need Cycle. A junct raider does not often have a regular cycle due to the tendency to take a Kill at Turnover (the halfway point in the Cycle) instead of enduring Need for 14 days more.
A transfer or Kill may be taken at any time after turnover, and in some pathologies or pregnancy even before Turnover, which will rephase the cycle, though that is not healthy and is resisted by all except Freeband Raiders. Life expectancy increases with the increasing intervals between Kills, up to but not exceeding the optimum length, which varies individual to individual. Since mutation continues to occur, and not all sub-mutations that breed true have been identified and characterized, the Tecton determines an individual's Need Cycle by experimentation (Farrises are best at making these judgment calls) and adjusts the interval between transfers throughout the Sime's life as the person ages or experiences stresses (such as pregnancy, major injury or disease.)
Augmentation burns selyn at increased rates, decreasing the time until new selyn must be acquired.
(Source: NOTES TO COPYEDITOR / To Kiss or To Kill) “Need” is used only to refer to a Sime’s monthly need for selyn, not to a need for money or food or love or anything else. If someone uses the word metaphorically to refer to something else, there is a reference to that fact in the text.
Source: Index card file. "Need Cycle" -- letter from Jacqueline to Marion Zimmer Bradley -- January 7, 1975) Any sime can be characterized as a "sane, level-headed, manic depressive." The most important determinant in how a sime character will react to a given stimulus is where he is on the need cycle.
Post-transfer to turnover is a diminishing manic segment. Turnover to Need is increasing depression and paralysis, unless the transfer will be a Kill. In a junct, pre-transfer is aggressive. Occasionally, you'll see the aggressiveness in a disjunct. VERY occasionally in a non-junct, and then it's shameful, disgusting, obscene. Digen (and sime) knows just how much (being sane) distortion of reality his senses and emotions are giving him on any given day in his cycle.
In sime calendar, each day of the cycle has a distinctive name.
Unhealthy: Under shorting, Digen's swings gradually leveled out to constant depression only mildly disturbed by transfer.
Healthy (Supported by good Donor): Manic segment becomes solid optimism, no challenge too big. On the need half, an energized skittishness, an instability which sometimes reacts one way and sometimes another to any given stimulus.
See: Unpublished Background for more information on other topics.