The Hold-Down Timer used in Distance Vector protocols:

A.
Sets the time limit of how long a router may keep a packet in its buffer, if the routing protocol is in the process of converging.

B.
Determines the number of seconds a router will wait before sending another update to neighbor routers.

C.
Sets a specific period for routers to neither accept nor advertise a route from a destination where an original route was recently lost.

D.
Sets a duration where routes are not accepted from the neighbor router that caused a routing loop.

Explanation:
http://distancelearning.ksi.edu/demo/520/ch06a.html