Query SCCM installation OS date (from one date)

Hello,

I want to make a collection for machines with OS installed from just one date. For example: I want a query for alle the machines that are installed from 11/20/2015. I found a query that show me the results for machines with OS installed in X number of days, but I look for just another one...

This is what I found:

select SMS_R_SYSTEM.ResourceID,SMS_R_SYSTEM.ResourceType,SMS_R_SYSTEM.Name,SMS_R_SYSTEM.SMSUniqueIdentifier,SMS_R_SYSTEM.ResourceDomainORWorkgroup,SMS_R_SYSTEM.Client FROM
SMS_R_System inner join SMS_G_System_OPERATING_SYSTEM on SMS_G_System_OPERATING_SYSTEM.ResourceId = SMS_R_System.ResourceId
WHERE
dateDiff(dd, SMS_G_System_OPERATING_SYSTEM.InstallDate, GetDate()) < 7