Each vitamin usually has recommendations on when to take it and how (i.e. how many times a day, with food, without food, with water, with any liquid). Our metabolism slows in the evening so this is the best time to take supplements if you want maximum absorption. However it's important to keep in mind that your body can only absorb so much at a time so, all other things equal, I think it's best to take supplements throughout the day, especially if you are taking multiple dosages of the same supplement.