Some harnesses are for fall arrest only, and not recommended for suspension for prolonged periods of time. Suspension Trauma is brought on by being suspended or immobilized in the harness for a length of time. This time varies from individual to individual due to how susceptible they are.
Refer to the AS/NZS 1891-4: 2009 recommendations concerning suspension trauma.
Any work that needs to be performed for prolonged periods of time while being in a suspended position, requires specially designed harnesses and equipment. Contact the manufacturer to ensure that you have the correct equipment for the required task.