I've got a BH90, and heard all of the surface recommendations from the dealer when I bought the tractor. I also read in the manual about what it says. I will tell you from experience that it doesn't matter. I drop my hoe on the ground in the woods out back, on a hill, just because that's the most convenient place to put it, out of the way. The only problem I had was after the first time I disconnected it and left it for 3 days, the stabilizers leaked down anought that I could not get the subfram under the BH. This was when I found out the dealer did not make the hoses long enough to connect without the subframe being UNDER the BH. I had to tilt the back end of the tractor to get it under the BH by lifting the front end with the FEL. The dealer then got the tractor back to lengthen the hydraulic hoses under warranty.
Why warranty? Well, after I showed him in the manual where Kubota recommends you retract the stabilizers completely, after disconnecting from the tractor, and resting the BH on the ground, I asked him if he could tell me how to do it the way I am "supposed to" with the lines as short as they were. He took care of it for free.
Now it doesn't matter if it leaks down (no, I don't retract the stabilizers completely like the manual says), I just connect the lines and lift it up, then back the tractor under it. As far as the unlevel ground goes, it doesn't matter since I can make all of the adjustments with the BH hydraulics. I don't see any time difference in hook up or removal when on level ground vs. the hill I usually use.
Chris