Please note that my expertise is in the genres and subgenres of rock, singer-songwriter, synthpop, and the like. This answer may be different for EDM, hip-hop, or country artists.
There's not really a "best time", though Spring through Fall do tend to be the most popular times to release music. (May/June through Sept/Oct). Times to avoid would be the holidays: Late November (because of American Thanksgiving) through the New Year tend to be really slow for releases because no one is really paying attention due to the holidays. So while I'd say there's no tried and true best time, aiming for Spring through Fall is likely your best bet.
Angela Mastrogiacomo is a blogger turned publicist. As the founder of Muddy Paw PR and music blog Infectious Magazine, she works with exceptional emerging artists to tell their stories through the use of guest blogs, interviews, and spotlight features. Muddy Paw artists have seen placements on Alternative Press, Noisey, Idobi, Substream, New Noise, and many more. Follow Angela on Twitter or Instagram @Angela_Mastro or reach her at firstname.lastname@example.org