I'm glad you asked!
If your goal is to get (and stay) lean, the best times to eat (the right kind of) carbs are:
1) In the morning
-your body is looking for energy and glucose after fasting all night during sleep
2) Before your workout
-your body needs some energy to burn and use during the workout
3) After your workout
-you use your muscle’s stored energy sources - glycogen - during a workout, and carbs replenish it!
One important thing to keep in mind is not all carbs are created equal!
You'll find the details in Carbohydrates 101: How to Eat Carbs to Your Advantage, but here are the basics -
Carbohydrates are made of fiber, starch, and sugar, and the balance of those three things are what determine if the carb is healthy for you or not. Most processed carbs (like bagels, bread, and breakfast cereals) have unnaturally high amounts of sugar, which can translate directly into excess body fat, so you want to aim for natural, whole food sources of both simple and complex carbs instead.
Your healthiest carb choices are foods like fruit, vegetables, quinoa, brown rice, and steel cut oats.