  We aim to investigate variations in the arrival time of coherent stellar
pulsations due to the light-travel time effect to test for the presence of
sub-stellar companions. Those companions are the key to one possible formation
scenario of apparently single sub-dwarf B stars. We made use of an extensive
set of ground-based observations of the four large amplitude p-mode pulsators
DW Lyn, V1636 Ori, QQ Vir, and V541 Hya. Observations of the TESS space
telescope are available on two of the targets. The timing method compares the
phase of sinusoidal fits to the full multi-epoch light curves with phases from
the fit of a number of subsets of the original time series. Observations of the
TESS mission do not sample the pulsations well enough to be useful due to the
(currently) fixed two-minute cadence. From the ground-based observations, we
infer evolutionary parameters from the arrival times. The residual signals show
many statistically significant periodic signals, but no clear evidence for
changes in arrival time induced by sub-stellar companions. The signals can be
explained partly by mode beating effects. We derive upper limits on companion
masses set by the observational campaign.
