The transient mode of the hybrid communication system that includes two wireless information channels operating in optical and millimeter domains is considered for the first time. The accurate analytical method for analyzing the transient behavior of the hybrid system is developed. It allows us to analyze the transient behavior of the system in an operating mode, in the case of a failure one of the channels, and periodical man-made radio influences. The expressions for reliability indicators and performance metrics of the hybrid system are presented and numerical calculations demonstrate the proposed method.