Yes, they may choose to utilize any unused and available sick hours. The employer cannot require the employee to use paid sick leave, but if elected to be used by the employee the employer can require they be taken in a minimum of a two-hour increment. The total hours of sick hours to be used during the leave will be determined by the employee.
Additional paid sick leave may be available for reasons as indicated by the FFCRA Emergency Paid Leave Rights as updated in the April 2020 provisions.