Hours are the wrong yardstick
Having instructed at an airfield that has to fly a large circuit because of noise abatement I would have said about 12-18 hours to solo but now I instruct at an airfield with a very tight 800ft circuit and the time to solo has reduced.
The concusion that I have come to is the hours to solo may have reduced but the number of landings to solo has not.
As the part of the circuit that most people find the hardest to achive is the touchdown it is critical to get the highest number of landings per hour.
So if you want to go solo quickly find an airfield at which the circuit wont take you on a cross-country.