hi , you can make the card's UPDATE property different based on formmode, if the formmode is new, you can make update the text information , if it's changing or updating , set the update property to false, then it will not be changed .
If ( SharePointForm.Mode=FormMode.New, DataCardValue.Text,false)
hope that can help you.
I've tested on my sharepoint form ,it turns out that false goes to nonsense, but I try another way it goes correctly,
1st step set the sharepoint integration's onedit property:
Set(vartime,Label1.Text); EditForm(SharePointForm1)
which means if you're editing information, it well at first set the time related text to a variable,

2nd step:
the label that contains the time related text ,set the text property below:
If(SharePointForm1.Mode=FormMode.New, Text(Now(),"[$-en-US]yymmddhhmmss"),vartime)

that means if the formmode is edit ,then it will stay the originally text unchanged.