Great question! The short answer is, “well, it depends…” It depends on many things. Things like: What was the nature of the problem to begin with? How long have you had it and how severe was it? Which nutrients are involved? What other lifestyle activities are being practiced in order to help? Have you been actually taking the vitamins?
The nature of your problem and the root cause of it are both factors in your healing time. For example: if you had low energy due to stress, custom vitamins including the B-complex family would likely be helpful in a matter of days to weeks. If, however, your concern was dropping a few pounds, the vitamins for weight loss can help support increasing energy and fat burning right away, but their full effect likely will take a month or more before noticeable weight loss occurs.
If your symptoms have been with you for a long time, or they are quite severe, it is reasonable to expect that it might take some time for the body to heal. The vitamins can help here. For example, if you have had dry itchy skin for many years, the customized vitamin formula will be tailored to those needs, but if there is additional damage to the skin due to years of damage from itching/scratching, that result will take longer to heal even once the initial dry itchy trigger has been resolved.
Some vitamins are water soluble, some are fat soluble. Because the body is 70 some-odd percent water, water soluble vitamins (like Vitamin C and B vitamins) are able to be absorbed faster and easier, thus effects from these are likely to be seen on shorter timescales (days to weeks). However, they can also be easily cleared by the kidneys, so it is important to continue to take the vitamins every day. Fat soluble vitamins (like Vitamin A, E and D) because they require building up stores in fat tissue take longer to have their full effects.
The vitamins will help but can’t do the job all on their own. Take the weight loss example again, the custom vitamins play an important supportive role, but significant weight loss will not occur unless diet and exercise are incorporated as well.
So, bottom line, vitamins are not drugs, so you will need to be patient. They don’t work (nearly) instantaneously like pharmaceuticals. Rather, they help support the body to function better on it’s own. Broadly speaking, a well designed customized vitamin regime, coupled with healthful diet and lifestyle habits, is likely to have a noticeable action in ~4-6 weeks. As you can see, the vitamin’s effects are more gradual, but ultimately, those effects are more sustainable and are vital to reaching a great level of health.