The paper discusses explicit properties and the requirements that are to be verified, imposed upon software-intensive systems by their environment and by their users. Those systems are time-critical, may contain autonomous components, and may exhibit proactive behaviour. It is suggested that the analysis and verification of properties in software-intensive systems requires time-aware model of interactive computation. The authors of this paper claim that hitherto used time interpretation in computer science is too simplified, and several simultaneously maintained independent time counting systems is a necessary precondition for timing analysis of interactions. A feature space for comparing the existing approaches to interactive computing is suggested, and a potential candidate for time-aware model of interactive computation is discussed.