Freezer not freezing - cleaning coils?

Hello - recently (tonight) my freezer seems to have stopped freezing. It is still cold but the stuff in it is thawing out. I read online about cleaning the coils so I am doing that (turns out they were filthy - entire back/under fridge was filled with dust). How long after the cleaning should the freezer start working again? Should I attempt anything else to start freezing again? I don't want to lose all my good food :-)