  We aim to determine unique features that characterise the past evolution of
the progenitor of the Helmi streams through the analysis of star formation
histories (SFHs). From the 5D {\it Gaia} EDR3 dataset, we extracted local
samples of stars dominated by the Helmi streams, the Galactic (thick and thin)
disc, and the local retrograde halo. We did this by identifying regions in a
pseudo-Cartesian velocity space (obtained by setting line-of-sight velocities
to zero), where stars belonging to these components, as identified in samples
with 6D phase-space information, are predominantly found. We made use of an
updated absolute colour-magnitude diagram (CMD) fitting methodology to contrast
the SFHs of these samples to unveil distinct signatures of the past evolution
of a disrupted accreted system: the Helmi streams. To this end, special
attention was given to the correct characterisation of {\it Gaia} completeness
effects and observational errors on the CMD. We further investigated
alternative sample selections to improve the purity of our 5D Helmi stream
catalogues. We find that the progenitor of the Helmi streams experienced an
early star formation that was sustained for longer (until 7--9~Gyr ago) than
for the Milky Way halo (10--11~Gyr ago). As a consequence, half of its stellar
mass was in place $\sim$~0.7~Gyr later. The quenching of star formation in the
Helmi stream progenitor $\sim$~8~Gyr ago suggests it was accreted by the Milky
Way around this time, in concert with previous estimates based on the dynamics
of the streams.

Astrophysics of Galaxies