Yes that is pretty annoying (and exactly why I stopped people changing their names in the first place). I think the open period has been way too long, the next one definitely will not be that long.
So next time I will probably start the thread on the 1st of the month to let everyone know, but not let people change their username until a few days later. Then keep it open for only 2-3 days.
I will also think about limiting how often you can change. A minimum of an hour or more between changes seems sensible.