def find_participation_daterange(trips, min_dt):
    """
    Determine the time bounds for selecting user trips to remove any trips
    with inproper timestamps from a user's incorrect system clock.
    """
    first_date, last_date = None, None
    for trip in trips:
        if trip.start_local > min_dt:
            first_date = trip.start_local.date()
            break
    last_date = trips[-1].end_local.date()
    return first_date, last_date
