Train Schedule Nearest Departure

Requirements You receive a sorted list of departure times for one day, each written as HH:MM, along with the current time in the same format. Return how many minutes have elapsed since the latest departure at or before the current time. When the current time occurs before the day's first departure, use the final departure from the preceding day and account for the midnight rollover. Examples The 4:40 departure was 15 minutes before the current time.