When my eldest was in special care I was encouraged to express every 2-3 hours to build up my supply for when she was ready to breastfeed and to make sure there was enough milk stored for her to feed through the night.
When she was 2 days old and my milk was not yet in enough to feed her every hour I was asked if I wanted to give her donated milk or formula. She had one day of donated milk and I expressed so much more for her once my milk was in that when she left special care 3 weeks later I donated the entire drawer of expressed milk to the milk bank in the hospital.