Your acknowledgements might be the only part of your dissertation that your friends and family will ever read (and probably some other researchers in your field too).
While acknowledgements typically have a lighter tone than the rest of the dissertation, it doesn’t make writing them something you finish within 20 minutes.
So when you are planning to write your chapters, you need to understand that compiling everything into the entire dissertation might take some additional time. You’ll need to add not only your acknowledgements, but also your CV and make sure everything is in the same layout.
Sometimes I open an old dissertation from my research group, and I can really feel the despair of the final weeks of writing and getting everything finished speak through in the acknowledgements. While I can totally relate to those feelings, I don’t think it is necessary to show these in your dissertation. The feelings will pass once you defend, but those words will remain there.
My colleagues told me to write my acknowledgements early on, and I followed that advice. I wrote my acknowledgements in November, as I was preparing my first draft. And I’m very glad I did so before getting sucked into the frustrations and anger/sadness that can arise at later stages in the writing/editing process.
I’ve restated a few sentences, and I’ve added some people that I forgot to name, but the core of the text hasn’t been altered since November.
Therefore, if you are writing your chapters, don’t forget to write your acknowledgements!