Your compost should heat up to 110 to 160 degrees and this happens because of the microorganism action breaking down the material. If it doesn’t heat up to that- to 110 to 160 degrees- then it won’t kill the seeds from the grass and weeds that you want to get rid of. And it won’t break things down well enough. And it heats up a lot more in the middle and so that’s another reason you want to turn it occasionally to keep that process unified.
Normally what happens is when you add the nitrogen, it will heat up a lot in the first two or three weeks and the process is slower after that.