Hi Davide,
by "date identifier" do you mean the action menu that comes up when highlighting the small dark triangle to the top left corner of a module? If so, I am testing DNN 05.00.00 with Blog module 03.05.01 and experiencing the same behaviour: the menu comes up, but is rendered to the top left corner of the browser window. I will need to investigate deeper.
Or maybe by "date identifier" you are meaning the Archive control, that displays a little calendar with a list of months when entries were posted. Tthe Blog module ships by default with 5 controls: the Main View, the Blog List, the Blog Control, the Search Control, and the Archive. If you cannot find one of them in your install, it may had been hidden or accidentally deleted. Try checking the recicle bin, and find the instance to put back in place.
If this doesn't help, you can in any moment delete all the remaining module controls and add a brand new instance of the blog module to the page. This wil re-create all the five controls in your page.Don't worry about any data losses during this process: Blog module data is stored portal wide, this means that your blogs and entries will be available back even if you delete the module and add one new to the page. Let me know if you need any further help, or if you meant something else by "date identifier".
Best regards,
Dario Rossa