No, I do not think team building during employees time off is necessary. I think mandatory team building outside of work can cause the opposite effect and employees can harbour resentment causing poor morale. I do however think that some team building during work hours is necessary. It is important to feel connected to those you are working with. When the relationship is only professional it can be a challenge to be empathetic and relational. Take time to chat, get to know your co-workers and laugh with them.