had to do a BX25 recently, fan. Debris got up in there and took out the blades. Wouldn't have mattered if the blades were made of steel either, it'd just tear up more than the blades if they were.
Anyway...I took a new fan, split it, and went ahead with the install according to the link above. 3 hours 35 minutes from start to finish which included removal of the belly mower.
I have done them at work, basically with hand tools, in barely under 2 hours by lifting the engine and replacing the fan in one piece. The coolant takes longer than any other single sub assembly in this particular job.