The issue is that you have :login Date as a character column, and it contains the time data along with the date data. So when you compare it to ALstartDT, it is having issues. I suggest that you uncomment the line where you attempted to change the :Login Date to a numeric with a format of "m/d/y". It should slightly changed to look like
dt6:Login Date << data type(numeric) << modeling type(continuous)<< format( "m/d/y");
and then change your select where lines to
dt6 << Select where ((Contains(MyList, :Site ID)) & :Analysis == "G4");
dt6 << Select where (:Login Date >= informat(ALstartDT,"mm/dd/yyyy"),current selection("extend"));
Jim