  The time resolution of the second monolithic silicon pixel prototype produced
for the MONOLITH H2020 ERC Advanced project was studied using a femtosecond
laser. The ASIC contains a matrix of hexagonal pixels with 100 {\mu}m pitch,
readout by low-noise and very fast SiGe HBT frontend electronics. Silicon
wafers with 50 {\mu}m thick epilayer with a resistivity of 350 {\Omega}cm were
used to produce a fully depleted sensor. At the highest frontend power density
tested of 2.7 W/cm2, the time resolution with the femtosecond laser pulses was
found to be 45 ps for signals generated by 1200 electrons, and 3 ps in the case
of 11k electrons, which corresponds approximately to 0.4 and 3.5 times the most
probable value of the charge generated by a minimum-ionizing particle. The
results were compared with testbeam data taken with the same prototype to
evaluate the time jitter produced by the fluctuations of the charge collection.
