def fmt_time(t):
    """Format a number of seconds into a human readable time string of HH:MM:SS.FFF
    """
    h, rem = divmod(t, 3600)
    m, s = divmod(rem, 60)
    return "{h:02.0f}:{m:02.0f}:{s:06.3f}".format(h=h, m=m, s=s)