Those who were musicians, heads of Levite families, stayed in the rooms of the temple and were exempt from other duties because they were responsible for the work day and night.
NIV
These are the singers, heads of the fathers' houses of the Levites, dwelling in the temple chambers, free from other service because they were on duty day and night.
AMP
And these are the singers, chief of the fathers of the Levites, who remaining in the chambers were free: for they were employed in that work day and night.
KJV