Hi Roy,
To my understanding, you would like to disable the submit button if today is less than 7 days from chosen date? would that be correct? If so, could you check if this formula works for you?
msxsl:string-compare(xdDate:Today(), xdDate:AddDays(my:field1, -7)) < 0
where my:field1 is the xpath to the dat field for the chosen date.
Please let me know how it goes.
Regards,