def convert_words_to_numbers(tokens):
    """
    Converts numbers in word format into number format
    >>> convert_words_to_numbers(['five', "o'clock"])
    ['5', "o'clock"]
    >>> convert_words_to_numbers(['seven', "o'clock"])
    ['7', "o'clock"]
    """
    number_words = ["zero", "one", "two", "three", "four", "five", "six",
                    "seven", "eight", "nine", "ten", "eleven", "twelve"]
    for index, token in enumerate(tokens):
        if token.lower() in number_words:
            tokens[index] = str(number_words.index(token.lower()))
    return tokens