3 week or so for the test to accumulate (the so called kick-in).. But in truth.. you will notice it within a couple of days, especially if you frontload. IMO.
Remember - IT DOES NOT take 3 weeks or so for test to enter the blood stream. It takes just a day or so for the full amount to enter the blood stream. The 'kick-in' is the accumulation of previous shots that are still very much active...