from datetime import datetime


def time_of_day(start: datetime) -> str:
    """Get time of day period"""
    s = start
    if s.hour < 4:
        return "Night"
    if s.hour < 9:
        return "Morning"
    if s.hour < 16:
        return "Day"
    if s.hour < 21:
        return "Evening"
    return "Night"