I'm not a big fan of the short SNCs that end at 11 EST. There are some contests, namely guessing contests, that do not need to be open for a full 24 hours. After all, these contests are pure luck and take little to no time or skill.
However, video contests that require setup, filming, and possibly re-shooting should not be shortened as it puts a rush on the entries, to the point where you were either able to perform beforehand or you aren't, there is no time to practice.