I had been planning to use it at night but I've read it is more effective during the day. Or do you have to use it night and day to be more effective? I'd rather use it only once to avoid having too many products on my face all the time. Also, how long do you have to wait after applying Vitamin C, before applying your daytime moisturizer and sunscreen? Is it ok to apply lotions with other antioxidants on top of the serum, will that "negate" any of properties of Vitamin C?