The category 'Date and time functions' is now translatable.
https://wiki.documentfoundation.org/Documentation/Calc_Functions/List_of_Functions
Also, remember that there are many templates to translate:
https://wiki.documentfoundation.org/Template:DatabaseFunctions-CommonSummaryText
Note: when working on the templates, you can not ignore tags like <noinclude> in the translated strings. Please keep all these special elements that appear in the source strings. If you don't, you will break the translated page.
Ilmari