Even so, it's probably not going to be super-effective, unless each workplace is willing to have enough useful small things that do not require knowing substantial chunks of the existing code base.
It is probably realistic to expect someone to write something useful (although possibly small) in three days. It is less realistic to expect someone to write a useful component integrated in a large system that they have to learn, in three days.
It is probably realistic to expect someone to write something useful (although possibly small) in three days. It is less realistic to expect someone to write a useful component integrated in a large system that they have to learn, in three days.