According to the real-world observation that firms can introduce consumer participation in different stages of product development, we assume that a consumer has private information on his/her preferences and build two signaling game models to capture how the consumer signals his/her true preference to a firm via their participation respectively in the front- and the back-end stages of product development. With these two continuation signaling games, we analyze the optimal timing decision of the firm (i.e., the choice between the front-end or the back-end stage in its product development to introduce consumer participation). This modeling helps to answer the question of under what condition the firm can introduce consumer participation in the front-end (the back-end) stage to truthfully signal his/her preference and then produce the consumer’s preferred product. With the equilibriums, we obtain the following main results. (1) The separating equilibrium requires the firm to share (seize) the consumer’s negative (positive) net participation utility in the front-end participation case, while this is not necessary in in the back-end participation case. (2) There are some parameters (in terms of consumer’s bargaining power and net participation utility) such that both the front-end and the back-end participation can induce the consumer to truthfully signal Ahis/her preference, but there also exist parameters such that only one of these two choices can induce the consumer’s truthful signaling. (3) Under the condition that both the front-end and the back-end participation can induce the consumer’s truthful signaling, the firm chooses the former (the latter) when the net participation utility is positive (negative).