def _timecalibrate(inst, disperser):
    """
    Get number of time slots needed for calibration

    Parameters
    ----------
    inst : string
        instrument

    disperser : string

    Returns
    -------
    int
    """
    ntcal = 0
    if 'GMOS' not in inst:
        if 'Mirror' not in disperser and 'null' not in disperser:
            ntcal = 3
    return ntcal