Final answer:
PTSD occurs within a variable time frame after a traumatic event, which can range from immediately to years later.
Step-by-step explanation:
PTSD occurs within a variable time frame after the experience of a traumatic event. It can begin immediately after the event or can take weeks, months, or even years to develop.
According to the research mentioned in the references, individuals in lower Manhattan experienced posttraumatic stress symptoms 2-3 years after the September 11, 2001 terrorist attacks. Similarly, Vietnam veterans were followed up for 14 years, and risk factors for posttraumatic stress disorder were examined.
Therefore, the correct answer is d) Not specified, as the time frame for developing PTSD can vary greatly.