Cannabidiol (CBD) has many medical uses, treating both mental and physical illness. The Food and Drug Adrministration (FDA) has approved one CBD drug called Epidiolex to treat seizures.  As more research is being conducted, scientists have discovered a range of uses for CBD in people of all ages. There are a couple of factors you need to look at when determining the best time to take CBD. The first being what medical condition is being treated. The second being the method of taking CBD.
A study on CBD found that insomnia has become a frequent reason for use. In the past, people suffering from lack of sleep or insomnia had not self-reported much CBD use. In this study, the majority of insomniacs used CBD in the evening while only few used CBD in the morning. People self medicating for insomnia found CBD more effective as a treatment when used before bed. 
In the study, anxiety was the most common use for CBD.  The majority of people self medicating for anxiety reported CBD use in the morning. Less people used CBD at night. People who take CBD as treatment for anxiety have found that taking it in the morning before facing their triggers is an effective treatment.
Ways To Take CBD
There are many forms of CBD and many ways to take it. The most common are oils. The oils can be placed under the tongue allowing CBD to directly enter the bloodstream. Other forms like gummies, take longer for your body to process. 
Since CBD is used to aid a variety of illnesses, the best time to take CBD varies person to person. If you are trying to determine the right time for you, focus on what you are treating and how soon you want to feel the effects of CBD.
References: Moltke J, et al. Reasons for cannabidiol use: a cross-sectional study of CBD users, focusing on self-perceived stress, anxiety, and sleep problems. J Cannabis Res. (2021) ; 18;3(1):5. doi: 10.1186/s42238-021-00061-5. PMID: 33602344; PMCID: PMC7893882. [Times cited=10]
 VanDolah HJ, Bauer BA, Mauck KF. Clinicians’ Guide to Cannabidiol and Hemp Oils. Mayo Clin Proc. (2019) ; 94(9):1840-1851. doi: 10.1016/j.mayocp.2019.01.003. Epub 2019 Aug 22. PMID: 31447137. [Journal impact factor = 4.87] [Times cited=35]
 Peter Grinspoon MD. Cannabidiol (CBD): What we know and what we don’t. Harvard Health. https://www.health.harvard.edu/blog/cannabidiol-cbd-what-we-know-and-what-we-dont-2018082414476. (2021)