It can take 4 months or longer from submission of DS260 to interview, and as we see in someone else's case right now if you miss the normal scheduling window even if the DS260 is processed then for high numbers you may not get an interview. So if your case number is at all likely to be current from say March then yes you could miss out by waiting till its current to submit. Like mom, I am curious as to why you would do it this way. There is a reason the instructions for selectees tell you to submit as soon as possible.