Also funny to imagine their scientists dismissing Earth as possibly habitable- "spinning around and around like that would result in impossibly complex weather systems - no way that's stable enough to sustain life!"
If so, they could easily measure "one year", and possibly subdivide it further, based on either consistent angle-measurements or roughly-similar chunks based on designating constellations and when they vanish or reappear.
My napkin math yields "as short as 1/3 Earth year", however I'm not sure I'd call that much^2 shorter, given some of the variety out there.
I'm eyeballing the graph in the linked blogpost, which has a dashed line for 4.5by solar-system age versus the optimistic "habitable" ranges. In particular, minimizing the distance gives (distance=0.4, star_mass=0.4) and trading off a bit for a more massive star (distance=0.5, star_mass=1.0).
The period of a circular orbit is proportional to (distance^3 / star_mass)^0.5 [0], so when I plug those pairs in I get orbital periods of ~0.4 to ~0.35 Earth years, respectively.