Hawaiian Electric Co. has signed up 471 customers in just a week for a program that will charge residential customers less for power used during the day — when solar energy production is highest — and more at night, the utility confirmed to Pacific Business News on Thursday. At the current rate of sign-ups, the program would reach capacity in just over two months. The time-of-use rate program, developed under the direction of the Hawaii Public Utilities Commission, encourages customers to use…