In Douglas Adams' Dirk Gently's Holistic Detective Agency, Chapter 2, when talking about how long the Electric Monk believed silly things, the book says:
How long did the Monk believe these things?
Well, as far as the Monk was concerned, forever. The faith which moves mountains, or at least believes them against all the available evidence to be pink, was a solid and abiding faith, a great rock against which the world could hurl whatever it would, yet it would not be shaken. In practice, the horse knew, twenty-four hours was usually about its lot.
I think the last sentence basically says that the Monk had believed for about twenty-four hours, but I'm not sure about the usage of "about its lot". What is the "lot" referring here, or is it some kind of idiom I'm missing? Googling it returned some vague Bible references and it doesn't seem to be what I'm looking for.
You can find the whole chapter here, if it helps at all.