  Accreting in the first few million years (Ma) of the Solar System,
planetesimals record conditions in the protoplanetary disc and are the remnants
of planetary formation processes. The meteorite paleomagnetic record carries
key insights into the thermal history of planetesimals and their extent of
differentiation. The current paradigm splits the meteorite paleomagnetic record
into three magnetic field generation epochs: an early nebula field ($\lesssim$5
Ma after CAI formation), followed by thermal dynamos ($\sim$5-34 Ma after CAI
formation), then a gap in dynamo generation, before the onset of core
solidification and compositional dynamos. These epochs have been defined using
current thermal evolution and dynamo generation models of planetesimals. Here,
we demonstrate these epochs are not as distinct as previously thought based on
refined thermal evolution models that include more realistic parametrisations
for mantle convection, non-eutectic core solidification, and radiogenic
$^{60}Fe$ in the core. We find thermal dynamos can start earlier and last
longer. Inclusion of appreciable $^{60}Fe$ in the core brings forward the onset
of dynamo generation to $\sim$1-2 Ma after CAI formation, which overlaps with
the existence of the nebula field. The second epoch of dynamo generation begins
prior to the onset of core solidification, suggesting this epoch is not purely
compositionally driven. Planetesimal radius is the dominant control on the
strength and duration of dynamo generation, and the choice of reference
viscosity can widen the gap between epochs of dynamo generation from 0-200 Ma.
Overall, variations in planetesimal properties lead to more variable timings of
different planetesimal magnetic field generation mechanisms than previously
thought. This alters the information we can glean from the meteorite
paleomagnetic record about the early Solar System.
