The key factor is air circulation. If your kegger has a fan in it the temperature of the fermenter will come down much faster. But 24 hours would be the max. for just about any setup.
I'm one of those bad people that pitches lagers warm and then starts the cooling process. Gets through the yeast growth phase faster.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk