Hello suske,
what do you want exactly:
Should the vi know the number of days per month? Or do you just want to have the number of days between 2 dates? Or do you need just a date string like '1. Feb. 2006'?
Anyway, there are functions in the time&dialog palette to do this:
"Date/Time to seconds" and "Seconds to Date/Time". You can setup your
own date in a date record and manipulate it...
Best regards,
GerdW

using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019