Cut a larger hole. Then place a 1/2 in. piece of ply on top overlapping the existing hole. Now cut your 24 in. hole in that and mount! Problem solved. Been there did it and it works great. By doing this you have raised your benchwork 3/4 inch. You will now need to use thinner foam but it essentially gives you the 3/4 inch of the benchwork back. I used 1/2 inch plywood and 1/2 inch foam on top. Now turntable mounts thru 1 inch and you can use bolts with nuts or washers as they suggest to adjust turntable flush!
Curtis