A educated guess:
475 helicopters are flying EMS missions in the US. Average is 1000 hours per year.
475,000 hours.
1900 EMS pilots fly an average of 250 hours per annum.
475,000 hours.
50% of flight time is at night.
237,500 hours.
EMS missions account for 80% of R/W night flights. Add 52,250 hours for other uses.
Total: 289,750 R/W night hours flown in the US per year.
