I bet every musician in the world has once asked "how often should you release singles?" to their manager or an industry label executive. The truth is every single release strategy has it's positives and negatives.
By asking how often should artists release music, you're asking for someone else's subjective view instead of resting your own experiments on how to release a song.
You can choose weekly, fortnightly, monthly or even a 6 week spread. Personally, I've been working on a model to share soon called the 42 Day Calendar but that's for another day!