2 Acres here, had the same exact issue. Started with a wheel horse 18 hydo, all the attachments, (Kept, is and still in use for snow blow).
Moved on and got a BX 23 with a 60" MMM, used this a a back up, as I really want to keep the hours low on the BX,particularly since it has the BH and FEL.
Then the wheel horse started to nichol and dime me, belts ,switches, pulleys, ect.So Iused the Kubuta in a pinch, while working on the wheel horse.
Bota works ok, its a bit tall, ROPS catches a lot of trees, its a bout the same time as the wheel horse because of its size 48" VS 60". It is also considerable heavier, so I cannot get as close to the pond edge, even with the additional 12" of cut on the Bota.
SO NOW WHAT YOU ASK ABOUT. The ZTR
I purchased a new Exmark Lazer 'Z" in 09, its faster than anything I own when it comes to mowing. I went with a 54"cut as I have stones walls and some tight tree areas on my 2 acres. The hills can be a bit tough, particularly if its wet. I still cannot get real close to the pond edge, so I get the wheelhorse out for some areas.
It took me -2.0-2.5 hours with the horse, bout the same with the bota, but nicer cut
the ZTR takes about 45 minutes to 1.25 hours depending.
The variance depends on weed wacking. With the other mowers, my wacking time would be 2-3 hours around the pond, trees, walls, flower beds with mulch, etc. I found with the ZTR my wacking has been reduced considerably so if I mow 1.25 hours on the ZTR as I metioned above, I may wack 30 minutes, most of that time is round my 1/2 acre pond, If I mow 45 minutes on the ZTR, wacking time is less than 1.5 hours.