Almost always in one day, then over and over until I manage to absorb as much of the jokes/notions that Terry put in. In one article he says that there are as many as 5 jokes per page and that one would have to be mad to take them all in at one go.
I keep finding more humor and knowledge from each of the books. lordy, I think I re-read Nation about 15 times. I am currently working on Witches Abroad, Wyrd Sisters and Reaper Man. Being a "shut-in", I have time every night. Sometimes I find myself at 4 am still reading and must force myself to go to sleep.
Aha! So, Bob's yer uncle... very clever.