You can leave early in the morning from Shenzhen to Foshan and come back to Shenzhen at night. Major coach stations in Shenzhen all have regular buses to Foshan, such as Luohu Coach Station, Qiaoshe Station nearby Luohu Coach Station, Futian Coach Station, etc. Choose the nearest one to your place. You can leaving around 8am in the morning and the last bus back from Foshan Coach Station to Shenzhen leaves before 9pm.