If you have only one time a week it's important that everybody does his homework. When I study a solo at home it takes me about ten minutes to play it in the rehearsel room, if everybody else also worked it out. If not it's going to take much more time. Sometimes there are shows with not so much pressure on it. Then we do not practice more. But before an important show we practice a few days before. Also we do extra excercises with the vocals, this can be easily done at home and not everyone has to be with it.