def create_greeting(moment):

    """Prints customized welcome string based on time

    Args: 
        moment      (timestamp):  current time

    Returns:
        greeting    (string):     the final welcome string

    """

    if moment.hour < 12:

        greeting = 'Good morning'

    elif moment.hour < 20:

        greeting = 'Good evening'

    else:

        greeting = 'Good night'

    return greeting