My spies inform me that there are engineering works running this particular Sunday.
We will now be catching the 10:06 bus from Brighton Station which will take an extra 20 minutes to reach Balcombe Station. Same meeting point with a prompt depart to give us time to walk through to the bus departure area at the back of the station.
We will return from Haywards Heath station where there are limited trains and additional buses. Fare is under £8, about £6 with a railcard.