When taken as prescribed, Valium usually begins to work within 30 minutes. However, the full effects of the drug may not be felt for 2-3 hours. The length of time it takes for Valium to kick in can vary depending on several factors, including the person's age, weight, and metabolism. If you are taking Valium for the first time, it is important to start with a low dose and increase gradually as needed. This will help you to avoid side effects and ensure that you get the most benefit from the medication.