potency of the benzo can be a factor, as strong benzos like temazepam, nimetazepam, and nitrazepam can cause onset physical dependence and withdrawl symptoms such as anxiety, dysphoria, and insomnia in as little as a week.
4 weeks of daily administration of a benzo can induce moderate physical dependence in (i think)26% of users.
less potent benzos(less binding affinity) such as oxazepam or quazepam may take longer to develop dependence with dependence being less severe than that of stronger benzos like alprazolam, temazepam, clonazepam, or diazepam.
half life, potency(binding affinity), pattern of usage(daily use, dose, etc.), and individual body chemistry are the factors that determine physical dependence.
however, psychological dependence can start from the first time(as with other recreational drugs). some people experience more euphoriant and relaxing effects than others, and therefore are prone to use more often. stimulant addicts often use large doses frequently to combat comedown effects, and may develop both psychological and physical dependence quickly.
those with personal or family histories of alcoholism or sedative dependence may be more at risk for addiction.
dependence can occur(and often does) from theraputic use, even at low doses. this problem is common with those perscribed benzos for insomnia or general anxiety disorder. due to tolerance that can rapidly build, some raise their doses or use them against medical instruction. its not unheard of for a once responsible, prescribed user to turn into an addict through the nature of benzo tolerance or to avoid "rebound" anxiety or insomnia.
*also: psychological dependence can occur quickly(faster than physical), and the habit of using benzos often develops to the point of lack of self control and constant build up of tolerance leading to physical dependence "creeping up" on the user. this could cause repeated higher doses to stop physical withdrawl, and addiction from that point tends to "snowball" up to severe addiction.