def from_min_to_day(time, organisation=None):
    """
    Convert a str time with minutes as a unit (i.e. a task duration), into
    another str rounded time with an 8-hour day as a unit.
    If an organisation is given as parameter, we use its field `hours_by_day`
    to know how long a working day lasts.
    """
    if organisation is not None:
        hours_per_day = organisation["hours_by_day"] or 8
    else:
        hours_per_day = 8
    day_estimation = int(time) / 60 / hours_per_day
    return str(round(day_estimation, 1))