There are a lot of differing opinions on when is the best time to move cattle after breeding, but one could say "never" is the the best time. These time frames are very arbitrary. It really depends on what kind of changes the cattle we be going through during the move. Are they going to be changing from a drylot situation to a lush green pasture, the cattle's disposition, the distance of the haul, the temperature and humidity during the move, etc.
In the end, every time you move cattle, or make changes, there is risk. You have to do what best works for your resources you have, and the constrains in which you have to manage within.