It depends on the dose of the pill and how you take it. 4 hours is a good guess, plus the time between ingestion and when it kicks in (varies a lot based on metabolism, food in stomach, etc., but probably 30-60 min or so if you just pop the pill). Crushing the pill up (or just breaking it into a few pieces) will make it hit faster and stronger, but supposedly that also shortens the duration a bit, and the powder tastes horrible. You can snort it, too, but I don't recommend it since it's so easy just to swallow a pill.