How long does it approximately take from the start of planning until approval?

After submitting the building application to the building authority, the processing there alone takes a good 6 months.

For us it was 3, so half.

After that, the house builder usually gets another 2 months of scheduling time before it actually starts sometime.

What is that supposed to be, "scheduling time"? Certainly not a standardized term, we don't know it, it didn't exist.

Total construction time 2-3 years.

For us it was exactly 6.5 months from the first bucket of the excavator to moving into the finished house. It can certainly go as you say, but your post comes across to readers as very "definite" or set in stone, which it certainly is not but your own experience. By the way, have you even built before? According to your other posts one might suspect you are still in the middle of it.

After submitting the building application to the building authority, the processing there alone already takes a good 6 months.

With exemption, it was two weeks for us from the submission of the documents until the start of the earthworks.

After that, the house builder usually gets another 2 months of scheduling time before it actually starts at some point.

For what?