Where and when were the African Slaves permitted to gather sing and dance?

They weren't. Their owners did not want to be seen with them if he didn't have to. This caused many owners to lose touch with their slaves, and in their free time, when they knew he wouldn't be around, they would sing and dance. Owners wanted their slaves to have children because the children would become their slaves, when they grew up. This allowed them to buy less slaves and save money.