Probability distributions functions (PDF) of the quenching (top) and formation (bottom) lookback times for our z > 3 quiescent galaxies observed with MOSFIRE. For each quantity we show the average of the individual PDFs with a solid line, the mean of the population with a darker vertical line (error bars are the error on the mean), as well as the distribution of values measured in a z  =  3.5 snapshot of the MERAXES semi-analytic model (SAM) with a dashed line (the dashed vertical bar indicates the mean value for the MERAXES galaxies).