Agree with bearcat - 10-20% of population at any one time will have gall stones.
But, even if you are asymptomatic JAA will require you to have the key hole operation (as they are small and thus pose a risk to in flight incapacitation). WRT how much time off - I'm unfamiliar with the CAA, but JAA say up-to 3 months - although this can be at the discretion of the medical examiner. If they are open to negotiation - point out: key hole surgery & they will have used CO2 for the surgery and thus would probably be fit to fly in reality within a month .... but whether the CAA will see it that way or not .. who knows.
We clear pax to fly within 10 days!