You don't have to hold the handle down in order to float, you just have to hold it down for a few seconds after the implement hits the ground. The 3point lift cylinder retracts a lot slower once the implement is on the ground but it will still retract as it is not pinned to the lift arms(you can make it drop faster if you play with the drop rate know in front of the seat but it is hard to get back to where you had it set). This is most easily shown with a plow or cultivator: stop forward motion of the tractor, lower the implement until it is on the ground (if you let go of the lever now and drive ahead it will stay on the surface), now before you pull ahead hold the lever in the lower position for say 15seconds (longer than is really needed but will make sure the lift cylinder is retracted, then release the handle and start driving forward and the plow will dig into the ground(without holding the handle).
So I have been working with my back blade on some projects, I have found that holding the handle down after the blade touches the ground for "any" period of time does nothing. There are two ways to keep the implement on the ground on uneven terrain on a GC1705, you either have to drop the implement on the ground in a low spot that in lower than the tractor or hold the drop/lift handle down indefinitely, there is no other way on these small tractors, they are limited as far as three point hitch capability..