According to "generation theory", present-day high school students born between 2002 and 2006 belong to Generation "Z", according to "generation theory". Previous research has proven that Generation "Z" spends a significant amount of time on digital media, which they usually access via smartphones. This research paper aims to determine and analyze how high school students' media habits correlate to their time management skills and academic success. A research methodology is quantitative and has been conducted on a stratified random sample consisting of 1478 Croatian high school students from 6 regions of the country attending different schools. Subjects of the research mentioned above are the following variables: media habits in smartphone usage, attitudes and opinions about time as a limited resource and opportunity costs, short-term and long-term time planning skills, and grade point average in the previous school year. The primary hypothesis of this research is that Croatian high school students' habits and behavior in the use of smartphones impact their competencies related to time management. The research has shown that high school students use their smartphones more than they initially assessed. Students do not perceive time as a limited resource; however, they are aware of their tendency to "waste" time which can point to an understanding of time in opportunity costs even if they are not familiar with the concept. Croatian high school students spent an average of 5 hours and 11 minutes on a smartphone (N = 1478). The study proved that respondents who spend more time on a smartphone have statistically significantly lower scores on the subscales of short-term planning (r = -.192, p < .001) and long-term planning (r = -.112, p < .001), but the correlation is weakly expressed. Participants who spend more time on a smartphone also have statistically significantly lower scores of attitudes toward time (r = -.421, p < .001), and this correlation is moderately pronounced. The paper is expected to contribute to a better understanding of new media theories through an interdisciplinary theoretical framework of communication science and the economic sciences theories. In addition to examining Croatian high school students' media behavior in the use of smartphones in the context of time management, this paper proposes an economic model of monetizing the opportunity cost of time spent on a smartphone.