The question of what days to post on social media and when (time of day) has been a topic of much discussion. Answers vary depending on who you ask: Thursdays and Fridays late afternoon and evening; mid-week - Wednesday morning; first thing Monday morning, and it goes on.
My answer differs from many other social media consultants. There are two factors I encourage you to consider:
1. Is your business local or worldwide? Does your business cater to your local area or do your services reach a wider audience? As an example, a local hair salon located in Seattle, Washington may post at different times than a New York B2B consultant with clients in Asia. The Seattle hair salon isn't likely to get many customers from outside the area. Even visitors from outside the area will be expecting the salon to post within local business hours. It makes sense then for the majority of their posts to be within their local business days and hours. If they are open Tuesday-Saturday from 10 am to 6 pm, that's when I'd expect them to post. The New York B2B consultant however will not limit her posts to local New York time. She has clients in Asia and elsewhere in the world. If she only posts at local New York time, it's likely her clients in Asia won't see her posts. Since her audience is really worldwide, she can post any day at any time.
2. Test different days and times. If you think posting on a particular day or at specific times are best, test it. Try that and see what sort of engagement your posts get. Then test some different days and times outside of the norm for you. Did your posts get the same engagement? After you've tested and reviewed your results, you'll have a better idea if it really makes a difference when you post and you can adjust accordingly.
Don't jump on the bandwagon of posting only on a certain day or at certain times until you're sure it's right for you. For my business as a social media marketing consultant, I have clients all over the world and a large worldwide Twitter following. As far as I'm concerned, I can post any day and any time and get engagement.
What I have found seems to be fairly consistent - weekends are more for fun posts rather than business posts. Of course the weekend for my client in New Zealand starts on my Friday here and her Monday is my Sunday - so that could get tricky!
My advice: be consistent and spread your posts out - particularly on Twitter (morning, midday, evening). Consistency is more important than when you post.
P.S. I recently read Daniel Pink's book "When: The Scientific Secrets of Perfect Timing". No, he doesnn't tell us the perfect time to post on social media. It did give me some great ideas on how to be more productive in my work though. Check it out.