People have been using cannabidiol (CBD) for insomnia for a few decades already, and with great effect. Simply search the internet for anecdotal evidence that using CBD can knock insomnia on its head.
For instance, this mother reports the following on the Patient.info forum:
"While I have found the regular exercise and not drinking alcohol before bed helps my sleep quality, one of the best things I have recently discovered is taking CBD before bed. Adding this to my routine of regular exercise has given me the best sleep (when the baby lets me!)" 
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And another mom posting on 420magazine.com forum said:
"...insomnia was one of the things that the infused CBD...oil relieved almost overnight for my daughter. It vanished like the night-thief it was within days. She's since slept with ease, much to her relief. Her insomnia was related to severe anxiety, and she takes four doses a day. No real euphoria, just a sense of well-being." 
However, good clinical research is still in its baby shoes, and we don't know yet why and how CBD works for sleeplessness. Available data is promising, though, and with CBD, insomnia's days appear to be numbered.
In this article, we'll be looking at the available medical research, how much CBD oil is recommended for insomnia, and how to take it for the best effect.
The short answer is—as previously mentioned, we do not know enough about it based solely on current research. There is positive movement in that direction, however.
The University of Western Australia is set to study cannabis (of which CBD is a compound) as a treatment for insomnia in human subjects. This is a world-first clinical trial, and it will focus on subjects who suffer from chronic insomnia. 
Yet, there is enough clinical data to suggest that when using high-dose CBD, insomnia is reduced, depending on what the underlying cause is.
To quote from a recent review of the literature:
"CBD may hold promise for REM sleep behavior disorder and excessive daytime sleepiness, while nabilone [a synthetic cannabidiol] may reduce nightmares associated with PTSD and may improve sleep among patients with chronic pain.
Summary: Research on cannabis and sleep is in its infancy and has yielded mixed results. Additional controlled and longitudinal research is critical to advance our understanding of research and clinical implications." 
One study focusing on the sleep behaviors of Parkinson's patients suggests that CBD may help reduce Rapid Eye Movement (REM) sleep behavior disorder.
Normally, our muscles are paralyzed while we sleep, so we don't react to our dreams. When this happens, blood flow is diverted to the muscles, offering your brain time to rest.
In REM sleep behavior disorder, your brain doesn't get enough rest. It is caused by a condition called REM atonia, which makes people sleepwalk or physically act out while still asleep because they are reacting to their dreams.
Understandably, this can affect the quality of sleep and cause insomnia-like symptoms in sufferers. 
Another study indicates the helpful role of CBD for insomnia due to pain. Nothing is as debilitating as chronic pain, and CBD has long been touted as a miracle worker against it.
A 2008 review looked at the data available on the analgesic effect of cannabinoids and concluded that:
"Cannabinoid analgesics have generally been well tolerated in clinical trials with acceptable adverse event profiles. Their adjunctive addition to the pharmacological armamentarium for treatment of pain shows great promise."
So, CBD was shown not only to be safe and well tolerated, but it also showed promising results in treating pain when taken together with tetrahydrocannabinol (THC). THC is the other well-researched cannabinoid derived from Cannabis Sativa L. 
It takes a very small leap of imagination to conclude that less pain means better sleep.
Another way CBD may ameliorate insomnia is by treating another of its causes—anxiety related to trauma.
In a recent case study, a young patient diagnosed with post-traumatic stress disorder (PTSD) suffered from anxiety and sleep disorders. These contributed to the patient’s oppositional behavior and impaired ability to focus.
The girl tried numerous medications and supplements, but they were not fully successful in managing her PTSD symptoms, including sleep disturbances. 
After the study, the researchers concluded that the use of CBD oil was a safe treatment for reducing anxiety and improving sleep in the girl.
There are no easy answers to this question, as people tend to react differently to different doses of CBD. This is based on factors such as weight and age as well as the quality of the oil.
It has also been shown that small doses of CBD oil tend to promote mental alertness and a sense of well-being. It's mainly the higher doses that seem to help for improved sleep.
It would be safe to start with 25 mg of pure CBD oil and increase the dosage over time. Some people need very high doses (up to 600 mg) before they feel the effects of the oil, while others feel it helps them in smaller quantities.
Update: If you want a CBD formula specifically crafted for Sleep issues try our Liposomal Sleep Formula
When you specifically use CBD for insomnia, keeping the following pointers in mind could ensure success:
1. Choose a good-quality oil. Since the CBD and medical marijuana market is still largely unregulated in the U.S. and many other countries, snake oil merchandisers abound, unfortunately. Do your research on what constitutes a good-quality CBD oil, and buy accordingly.
2. Take the oil an hour before bedtime, on an empty stomach. This will ensure that you'll start to feel the effects when you need to, and an empty stomach increases absorption.
3. Take it with another oil. Unfortunately, CBD is not easily taken up by the body. However, it is hydrophobic, meaning that taking it with a teaspoon of coconut or olive oil—or even a good Omega-3 supplemental oil—will increase its absorption rate. MCT oil is the best carrier, that is why all SOL*CBD products contain it.
4. Drip the oil under your tongue. Taking the oil sublingually and keeping it in your mouth for a minute or two will also increase its absorption and ensure faster results. This is because the compounds will enter your bloodstream faster.
You can safely experiment with CBD for insomnia, so play with doses to find what works best for you. Don't replace any medication with CBD without the consent of your physician.