Temperatures will fluctuate and it will depend on where your air intake is coming from, if it comes from outside your house the temps will change throughout the day or night anyway.
I have to keep an eye on the temps and if its to hot i open windows to try to keep tepms down.
In my rooom temps can range from 25c to 30c and if its a hot day as high as 35c that is with two 600watt HPS.
The best thing is set up your room and try it all out first and see what the temps are like.