Software companies need to continuously deliver customer value, both from a short- and long-term perspective. However, software development can be impeded by what has been described as Technical Debt (TD). The aim of this study is to explore the negative consequences of TD in terms of wasted software development time. This study also investigates on which additional activities this wasted time is spent and whether different types of TD impact the wasted time differently. This study also sets out to examine the benefits of tracking and communicating the amount of wasted time, both from a developer's and manager's perspective. This paper reports the results of a longitudinal study, surveying 43 software developers, together with follow-up interviews with 16 industrial software practitioners. The analysis of the reported wasted time revealed that developers waste, on average, 23% of their development time due to TD and that they are frequently forced to introduce new TD due to already existing TD. The most common activity on which additional time is spent is performing additional testing.