The probationary period for an assistant professor starting his/her career without credit for prior professorial experience is seven academic years. The "tenure clock" is the commonly used campus metaphor for the imaginary meter that counts down this probationary period. Credit for prior professorial experience, discussed in a section above, can be thought of as analogous to moving the clock forward, and therefore reducing the length of the probationary period. At the end of the probationary period, a decision to promote and tenure is required according to the Laws of the Regents. A negative decision results in issuance of a one year terminal appointment. The purpose of this terminal year is to provide the faculty member ample opportunity to explore other career options, and to allow a transition period for the primary unit to adjust for the impending departure of the faculty member. 
There are occasions when the tenure clock is adjusted. This is generally referred to as "stopping the clock", although setting back the clock is a more accurate metaphor, and moving the clock forward also happens on occasion. Leaves associated with extended illnesses, accompanied by sick leave, parental leaves associated with childbirth, and family leaves are the most commonly accepted reasons for stopping the clock. Stopping the clock because of a leave does not prejudice the tenure and promotion review in any way.
A copy of the campus policy Adjustments to The Tenure Clock

Faculty members are urged to consult their department or division chair in all matters related to reappointment, tenure, and promotion. In addition, the Associate Vice Chancellor for Faculty Affairs (AVCFA) is available to faculty members needing assistance or explanation. The AVCFA can recommend workshops and mentors for faculty members seeking assistance in dossier preparation, building a teaching portfolio, and other matters related to the review and evaluation process.