A Time Course Event is the time taken by a specified drug to fully enter the user's system.
Barbiturate drugs are depressants, and are used medically as anti-seizure drugs or anesthetics; they are also used recreationally as "downers."
Dependence on drugs takes many factors into account, including speed of action, mental need, and physiological addiction. In this case, the speed of action can contribute several ways; a fast-acting barbiturate can be taken for a quick downer -- sleeping pills are examples of this -- while slow-acting ones are more suited for panic control or all-day stress relief. In the case of addiction, it becomes more a matter of how the speed of the drug meets the user's needs; despite the possibility of physiological addiction, a user is less likely to become addicted to a barbiturate that does not meet his mental or emotional needs.
On the other hand, if a user needs something to affect him all day, but takes a fast-acting, short-term barbiturate, he might continue to take them as each pill wears off. Even though the specific need is not met properly, the sheer number of pills will become familiar to the body, and more or stronger doses might be needed to fulfill the same purpose; thus, addiction.