Performance studies of the Time-of-Flight (ToF) subdetector of the ATLAS Forward Proton (AFP) detector at the LHC are presented. Efficiencies and resolutions are measured using data samples collected at low and moderate pile-up in 2017. While low efficiencies are observed, of the order of a few percent, the resolutions of the two ToF detectors measured individually are 21 ps and 28 ps, yielding an expected resolution of the longitudinal position of the interaction,
$z_{vtx}$ in the interaction region. This is in agreement with the observed width of the distribution of the difference between $z_{vtx}$
measured independently by the central ATLAS tracker and by the ToF detector, of 6.0 $\pm $ 2.0 mm.