Using Velocity points on Delta domestic - when to book?

We are planning a family holiday to the USA in April/May 2018
There’s 4 of us and we want to use our velocity points for domestic flights.
At this stage the dates we are after to get a flight from Lax to Mia it’s only showing connecting via Atlanta. I wanted either a Wednesday or a Thursday. The only direct flight is a Tuesday for several scattered dates in April.
Are they likely to open more as their calendars open or should I jump on it now? If we leave ona Tuesday it means extra time in Miami( expensive city) before our cruise. The thought of connections with Kids isn’t great but I’m just wondering if I should bite the bullet and seeing as I’m saving $1000 on flights just add the extra night or two in Miami
It’s such a gamble I don’t know how Delta works


Personally, I like to book award seats when I see them. As you never know when the seats would disappear. I booked with Delta on international business class when the tickets were released 11/12 mths in advance. Not quite sure when or whether they would release more seats.