  A tidal interaction between a star and a close-in exoplanet leads to
shrinkage of the planetary orbit and eventual tidal disruption of the planet.
Measuring the shrinkage of the orbits will allow for the tidal quality
parameter of the star ($Q'_\star$) to be measured, which is an important
parameter to obtain information about stellar interiors. We analyse data from
TESS for two targets known to host close-in hot Jupiters, WASP-18 and WASP-19,
to measure the current limits on orbital period variation and provide new
constrains on $Q'_\star$. We modelled the transit shape using all the available
TESS observations and fitted the individual transit times of each transit. We
used previously published transit times together with our results to fit two
models, a constant period model, and a quadratic orbital decay model, MCMC
algorithms. We find period change rates of $(-0.11\pm0.21)\times10^{-10}$ for
WASP-18b and $(-0.35\pm0.22)\times10^{-10}$ for WASP-19b and we do not find
significant evidence of orbital decay in these targets. We obtain new lower
limits for $Q'_\star$ of $(1.42\pm0.34)\times10^7$ in WASP-18 and
$(1.26\pm0.10)\times10^6$ in WASP-19, corresponding to upper limits of the
orbital decay rate of $-0.45\times10^{-10}$ and $-0.71\times10^{-10}$,
respectively, with a 95% confidence level. We compare our results with other
relevant targets for tidal decay studies. We find that the orbital decay rate
in both WASP-18b and WASP-19b appears to be smaller than the measured orbital
decay of WASP-12b. We show that the minimum value of $Q'_\star$ in WASP-18 is
two orders of magnitude higher than that of WASP-12, while WASP-19 has a
minimum value one order of magnitude higher, which is consistent with other
similar targets. Further observations are required to constrain the orbital
decay of WASP-18 and WASP-19.
