1. create an additional attribute in your participants table.
2. edit the settings of the plugin
You see, I called the date question "QDate".
3. Set the default value of the date question to this attribute
And the result is:
And in the next survey:
The text is done by micro-tayloring, like
{if(is_empty(TOKEN:ATTRIBUTE_1),"This is your first visit. Please, enter date and time","This visited us before. This date is entered below")}
You did not show us how you want to display this.
So you will have to adapt.
Joffm