I live on the east side of the U.S. and we are starting to get pretty chilling night time temps. I know they say you want to be done growing by the time your first frost comes, but are my babys that are well into the 5th week of flowering now gonna have any problems with cool nights that hit the lower 50's ??

Sir lower 50's are nothing to worry about. Cannabis can still live through a light frost. Once the weather gets down into the 30's I would start to worry.