In finite automata, there is no concept about time; or we can think in this way: cach move takes one unit time. But in reality (c.g., in designing an embedded system), timing is an explicit requirement which can be expressed through timers. Timers can be used to control moves of the automata. Investigate your ways of adding timers to the definition of finite automata (hence your extended finite automata are able to describe a simple class of real-time systems)