Date format in Custom field

Hi,

There is a very brief info on custom fields here:
https://docs.acymailing.com/main-pages/custom-fields/create-custom-field

All I find about dates, is that d%m%y will mean dd/mm/yyyy - not very useful for me.
I need the international format yyyy-mm-dd hh:mm:ss
In particular I need this to import subscribers - that I exported from AcyMailing.

Thanks!