The standard answer is "21 days" however the reality is no one knows. The IRS is so heavily backlogged that as of June 30th there were 35 million unprocessed returns. There are folks who filed their return in February who have not received their refund and are still seeing that first bar of Return Received. My original return was about a week later than usual but I had to amend at the end of March due to a 1098T finally coming in. I felt grateful that I could e-file that amended return until 16 weeks has passed (as of today) and there has been no movement. My transcript shows that my return has not been accessed, it still has the AS OF date of April 26th.
