The longer the unsupported length past the cutless bearing, the higher the risk of vibrations or bending the shaft if the prop catches something.
If it is running smooth, you don't have a problem with it, so you can make a call.
I have designed high-efficiency motor
yachts where I extended the stern tube out from the back of the keel
and pushed the shaft out a little as well to get better, cleaner water
to the propeller
. If the shaft diameter is big enough and the whole system well aligned, balanced and engineered, no problem.