Development of more complex cognitive systems during evolution is sometimes viewed in relation to environmental complexity. In more detail, growth of complexity during evolution can be considered for the dynamics of externally observable behaviour of agents, for their internal cognitive systems, and for the environment. This paper explores temporal complexity for these three aspects, and their mutual dependencies. A number of example scenarios have been formalised in a declarative temporal language, and the complexity of the structure of the different formalisations was measured. Thus, some empirical evidence was provided for the thesis that for more complex environments, more complex behaviour and more complex mental capabilities are needed.