  We present 17 transit light curves of seven known warm-Jupiters observed with
the CHaracterising ExOPlanet Satellite (CHEOPS). The light curves have been
collected as part of the CHEOPS Guaranteed Time Observation (GTO) program that
searches for transit-timing variation (TTV) of warm-Jupiters induced by a
possible external perturber to shed light on the evolution path of such
planetary systems. We describe the CHEOPS observation process, from the
planning to the data analysis. In this work we focused on the timing
performance of CHEOPS, the impact of the sampling of the transit phases, and
the improvement we can obtain combining multiple transits together. We reached
the highest precision on the transit time of about 13-16 s for the brightest
target (WASP-38, G = 9.2) in our sample. From the combined analysis of multiple
transits of fainter targets with G >= 11 we obtained a timing precision of
about 2 min. Additional observations with CHEOPS, covering a longer temporal
baseline, will further improve the precision on the transit times and will
allow us to detect possible TTV signals induced by an external perturber.
