Leave in condition as the name implies is a conditioning cream that's left in the hair to provide extra moisture to the hair, protect it from damage, and help detangle the strands. It is not advised to be used daily as it can cause build up of product on hair strands.
Co-wash on the other hand, is made with surfactant (washing agent) hence the conditioning purpose is not to be left on for more than 30 minutes, which is best used after the hair has been clarified, shampooed or washed. This helps to immediately restore the hair moisture.