Various articles have pointed to Tuesday as best launch day. I launched Growthhacklist on a tuesday and it was on the third place at the end with over 500 upvotes. So I think Tuesday is really a good day to launch your product. There are several platforms to submit your product.

1. http://www.producthunt.com/
2. https://betalist.com/
3. https://betapage.co/
4. https://madewithoutcode.com/
5. https://news.ycombinator.com/
6. Reddit channels https://blog.producthunt.com/how-to-launch-on-product-hunt-7c1843e06399