How long does it usually take for creon to work?for g.i. problems?

Very quick: Creon and other pancreatic enzyme preparations work within a few days when taken with meals to help you break down fats especially. Sometimes however the dose is not enough, do this may result in a longer time until symptoms get better while the dose is being adjusted.

Pretty quickly: Usually within a few days if taken in the right dose and for the right indication (chronic pancreatitis)