As you are posting in 'Calc' - you may like a formular, see:Convert UNIX timestamp
Will give you the Calc date value, then format to your needs (Format>Cells).
I have tried the extension 'DateTime2' but it appears not to handle multiple entries.
Sorry, please explain: you should be able to insert into a single cell, a range of cells, into multiple ranges.
Pls state OOo version and OS you are using in case of any error.
The extension does not convert dates... so it doesn't solve your question. The posting linked above should help you.