The half life of cardarine is 24 hours. You will start to see the effects the very first day but it'll take about 4-5 days to notice the full effects.
Cardarine isn't a stimulant so it won't 'hit you' the way a pre-workout or cup of coffee will. Rather, you'll notice a nice increase in endurance during your workouts. Cardio will seem much easier and you won't get winded near as fast.
You will start to notice the fat loss effects in your physique in about 1-2 weeks.