How is Last Thursdayism any more irrational than any other Young Earth sect? Several independent dating mechanisms show the Earth to be around 4,5000,000,000 years old. Assuming 4 days or 4000 years still miss the mark by some orders of magnitude.
Call me irrational if you will, but I have a whole lot harder time believing the earth's been around that long than I do believing the earth is young.
Maybe because it's not his favoured Young Earth model?
Still waiting for a satisfactory answer myself.