Probably never. See https://web.archive.org/web/20100714051425/http://www-spc.igpp.ucla.edu/personnel/russell/papers/venus_mag/
"It is important to note that, contrary to popular belief, dynamo theory does not credit the smallness of the magnetic moment to the slow rotation of Venus (a Venus day of ~ 243 Earth days is almost equal to the length of its year of ~ 224 days, and its sense of rotation is retrograde). It is also notable that Venus would not have maintained any remanent crustal magnetic fields from its proposed early period of dynamo activity because the temperatures in the crust are expected to be above the Curie point (below which such fields could persist in rocky materials)."
Earth's magnetic field is created not just by the spin of the planet, but by convection within the molten core. Venus may well have had an Earth-magnitude magnetic field for the first billion years of its life, but lost it once that convection ceased.
For the creation of artificial planetary magnetic fields, you might want to have a look at this: https://www.sciencedirect.com/science/article/abs/pii/S0094576521005099
It seems far easier to put a set of superconductors across the surface, or in orbit, than it does to restart core convection.