Nothing happens soon with IBS
2 months is the same as I waited. But you will have 'some degree' of certainty after that time. There may still be some blood/urine/stool tests they may do as well to try rule out other problems.
Dont fret too much, try and relax for now, Im not a doctor (obviously!) but from what research I have done, there is no illness, syndrome or even cancer that is going to get worse overnight.