A web-based tool in Microsoft 365 that enables users to quickly create surveys, quizzes, polls, and feedback forms.
Dear Green,
Welcome to the forum here.
I'm afraid that Microsoft Forms may not have such features. Generally, for the validation feature, you may use Microsoft Forms Pro with Regex Expressions.
Ten Regex Expressions To Use With Forms Pro
To use Microsoft Forms Pro, you may need Dynamics 365 Customer Voice which is a new name of Microsoft Forms Pro.
Transition from Microsoft Forms Pro to Dynamics 365 Customer Voice
However, it may still have some customization limitations. To fully meet your requirement in your environment, I suggest you use PowerApps instead of Microsoft Forms.
You can create the form as follows.
Type the formula If(DatePicker1.SelectedDate<=DateAdd(Today(),6),true,false) on Visible on TextInput1.
Result:
If you need more requirements, welcome to post back with your updates at your convenience for our confirmation.
Thanks for your effort and time!
Sincerely,
Cliff | Microsoft Community Moderator