import re
import time


def extract_time_diff(text):
    """
        Returns the difference between the current time and the time
        in the embedded << >> tag (encoded in POSIX time)
        or None if a matching tag cannot be found
    """

    time_list = re.findall('<<(.*)>>', text)
    if time_list:
        update_time = float(time_list[0])
        diff_time = round(time.time() - update_time)
        return diff_time
    else:
        return None