I keep my tank heaters at the bottom of the tank sideways as to not have to turn them off during a change. I replace with like-temp water, but if it's off a bit, then it will quickly get to the right temp. I would have the tank at the correct temperature prior to acclimating him, but there is no real reason to do that, it's just my opinion to have everything set and ready before adding in a new fish.
When acclimating a fish to a new tank you don't want to just do temp acclimation, you should also be doing chemistry acclimation as well as Spooky mentioned. While acclimating him/her to the chemistry you are also acclimating them to the temp at a good pace.
Personally I don't acclimate nearly as long as it is recommended.. but then again I have never lost a fish during an acclimation in nearly 20 years. I float in a cup, every few minutes or so I take a bit of old water out, replace with tank water.. repeat process a couple times so they are really only in the cup for 10-15 mins or so. The temps generally don't take long for mine to even out, as I'm at the point where I can get the new water to within a degree of what the tank is set at (like I said, nearly 20 years so I've learned to tell temp by feel lol). So my fish are just acclimating to any difference in chemistry/pH rather than temp.
So once you've had your guy for a bit and the tank is settled, it will take shorter time to do a change (and this is based off a tank 5+ gallons, cycled, etc). Anything smaller then you will most likely have to take the longer route to acclimate him to chemistry.