def time_to_kobo(y, m, d='01', h='00', mi='00', s='00'):
    """Format timestamp for Kobo."""
    y = str(y)
    m = str(m)
    d = str(d)
    h = str(h)
    mi = str(mi)
    s = str(s)
    return y + '-' + m + '-' + d + 'T' + h + ':' + mi + ':' + s + 'Z'