what do you recommend me ? write the bibliography as I write my dissertation, or focus on the bibliography at the end of the writing? Thank you
There are (mainly) two types of citations:
citations of methods/results by other researchers that you use in your work. These citations may appear anywhere in the document.
citations made to summarize the state of the art. These appear mostly in the introduction.
I would recommend adding the first type of citations as soon as you explain the methods/results you are using in the main text. It is very easy to miss some of these afterwards and forget to cite them, and you would be incurring plagiarism.
The second type of citations appear in the introduction, which is anyway usually written last. You can leave these citations for the end if you wish, though I still find it less time-consuming to just cite everything as I write the main text. Doing a "second sweep" of your text and trying to remember "what did I want to cite here again?" is bound to add some overhead.