MCM - System size calculation

Hi! I have a kind of strange quiestion I guess. Its from a exercise I got. We are studying a model called the Ising model which is model of a system where every site in the system can take values such as for example +1 or -1. We are modelling this with Monte Carlo Methods. The question reads as follows:

Consider a complete enumeration of a

L×L Ising model. What is

the maximum size L that would be possible to study in 24 hours

on a single 3GHz-processor. Base your answer on some reasonable

assumptions.

Can you give me some guidelines and tips maybe to approximate this?