In addition to the symptom triad of intrusions, avoidance behaviour and hyperarousal, typical and frequent characteristics of acute and chronic posttraumatic disorders are neuropsychological disturbances of working memory and executive functions. So far, however, only a very limited number of studies have dealt with their effects on the capability to assess time-related information. The purpose of this prospective study therefore was to compare persons after an acute traumatic experience with healthy controls in the course of 12 months, focusing on their ability to estimate time as a measure of their readiness of attention. 39 participants aged 17–59 years (mean age = 35.1 years, who had experienced a traumatic event and exhibited symptoms of acute stress disorder) were compared with 38 healthy controls (mean age = 36.1 years) at eight times of measurement within a period of 12 months. Performance was determined by means of a prospective time estimation task. The participants had to estimate a time interval of 5 s, once with and once without feedback about the quality of the estimates. The time estimates by the traumatised persons were significantly less precise than those by the control group. Progress analyses have shown that trauma patients exhibit larger deviations from the defined time interval, both under feedback conditions and without feedback. Psychological traumatisation leads to both an acute and long-term, demonstrable impairment of time estimation ability. The recognizable disturbance of information processing may both be a cause and a result of clinical trauma symptoms.