def _set_timelabel(obs, use_tref=True):
    """For a given observable, returns the timelabel to be used in plots

    Parameters
    ----------
    obs : Observable instance
    use_tref : bool
        whether to use tref (set False for stationary plotting)

    Returns
    -------
    timelabel : str
    """
    if obs.mode != 'dynamics' and obs.timing == 'g':
        timelabel = 'Generations'
        if obs.tref is not None and use_tref:
            timelabel += ' (since tref {})'.format(obs.tref)
    else:
        timelabel = 'Time (minutes)'
    return timelabel