There is no minimum time requirement between submission of application electronically and interview date particularly for non-immigrant visas. What you're hearing is all anecdotal stories.
Not only does the Department of State website not mention anything like that, I know people who have applied and gone for interviews within a couple of days. Hypothetically you can submit an application today and if you get an appointment for today you can appear for your interview.
With immigrant visa applications it is slightly different, after your petition has been approved by USCIS, you need to hear from the consulate that you can apply for a visa before proceeding.
Back in the day 90's when applications were purely paper based, the same date you submit your application you are interviewed, admittedly that is very long ago.