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tokens: about 200 Myr after the MS turnoff). The second phase coincides with the base of the RGB, where τ DR decreases from about 3 Gyr to about 100 Myr for both stars. These rapid changes in τ DR can be explained by departures from thermal equilibrium, which are measured by ε grav = − T ∂ s /∂ t . The bottom panel of Fig. 8 shows the variations in ε grav in the stellar core of both stars, which are clearly anti-correlated with the variations in τ DR . The forcing of differential rotation is maximal at the peaks of ε grav , that is when the core contracts on a thermal timescale. Fig. 8. Variations in the timescale τ DR over which differential rotation is forced ( top panel ) and in ε grav ( bottom panel ) along the subgiant branch for our best-fit models of KIC 8524425 (red dashed line) and KIC 5955122 (solid blue line). The filled circles correspond to the stars at current age. The stars studied by D14 all lie after the peak of ε grav corresponding to the base of the RGB except for the least evolved one (star B), which lies precisely at the maximum of the peak (see Fig. 6 of Eggenberger et al. 2019b ). As shown by Fig. 8 , the evolutionary stage of KIC 8524425 and KIC 5955122 places them well before the maximum of ε grav , which confirms that they are indeed less evolved than the sample of D14. The nearly solid-body rotation profiles that we obtained show that the internal redistribution of AM for these stars takes place on timescales lower than the current value of τ DR (about 320 Myr for KIC 5955122 and 570 Myr for KIC 8524425). 5.2. Efficiency of AM transport To estimate the efficiency of the AM transport that is required to reproduce the observed rotation profiles, we computed rotating models for the two subgiants, including an additional constant viscosity ν add in the equation for the transport of AM in radiative zones. This approach was already followed for instance by Eggenberger et al. (2012 , 2019b) , Spada et al. (2016) , and den Hartogh et al. (2019) , for more evolved subgiants and red giants. As already mentioned in these works, this is a very crude description of the AM transport in subgiants. Naturally, we do not expect whatever mechanism is at work to indeed operate like a diffusive process with constant viscosity. The main goal of this approach is to study how the mean efficiency of the unknown transport processes vary with stellar parameters, and in particular with evolution. It was shown by Eggenberger et al. (2019b) that the transport efficiency decreases during the late subgiant phase, near the base of the RGB, but must increase again as stars evolve along the RGB ( Eggenberger et al. 2017 ). We here had the opportunity to estimate the efficiency of the transport closer to the MS turnoff and compare with its value on the MS. 5.2.1. Rotating models We used two different stellar evolution codes: YREC ( Demarque et al. 2008 ) and GENEC ( Eggenberger et al. 2008 ). The two codes differ in their treatment of the rotation. GENEC