The ONLY answer to this question is WITH FOOD. You are wasting your money to take vitamins, especially the water soluble ones on their own. All you will get is expensive urine. Vitamins are processed by your body as part of the whole digestive process - your body is designed to extract it's own vitamins from the food you eat. Take supplements of any kind away from food and you are wasting your money.... The time of day is not important,
take your vitamin with water or food. i recommend that with any pills or vitamins you take them in the morning fully awake and not at bed time. this will ensure that you are fully aware if you are allergic to them.