Firms face opposing incentives regarding when to make strategic decisions about their exploration ventures. On the one hand, postponing a decision can reduce uncertainty, while on the other hand, moving quickly allows one to capitalize on favorable market conditions. Drawing on theories of entrepreneurship, real options reasoning, and decision speed, we suggest that firms resolve competing tensions between acceleration and deceleration through an assessment of their venture portfolio and environment. An empirical study of the timing of termination and exploitation decisions regarding 3,272 exploration ventures in Australia’s mining industry over the years 2002–2011 provides insights into the drivers of decision timing. We find that venture portfolio composition is an important driver of timing but only with regard to exploitation decisions. Higher levels of market uncertainty increase the time to venture termination but not exploitation, and a positive market trajectory increases the time to venture termination yet decreases the time to venture exploitation. We also find support for an interaction effect between the portfolio and market characteristics. This pattern of findings sheds light on the tension between acceleration and deceleration in strategic decision making and highlights the importance of distinguishing between the timing of different types of decisions.