Recently, a trend toward accelerating product development can be observed. However, there is still debate over whether firms should accelerate product development. While many empirical studies have been conducted to date, no consistent conclusions have been reached. Therefore, this paper theoretically examines whether firms should accelerate product development. The conclusion of this paper is that the question of accelerating product development depends on the situation, and the relevant situational factors include R&D efficiency, R&D costs, competitive dynamics, time allowed for R&D, and project quality. In general, acceleration is advantageous when a firm operates in a rapidly moving market (where product life cycles are short and less time is allowed for new product development), when it operates in a market where value differences between successive projects are small (i.e., developing new models rather than innovative new products), and when it belongs to a highly competitive industry. However, for firms with low R&D efficiency, it may actually be more advantageous not to accelerate. The conclusions drawn in this paper can explain why prior empirical studies have yielded contradictory results, and why the efforts of firms to shorten decision-making periods and the time required for product development are particularly prominent in certain industries. Additionally, this paper can assist specific firms in making decisions about whether to accelerate product development. The model applied in this paper is a type of R&D competition model, and game theory is employed for the analysis of competitive dynamics.