try this
Code:
Private Sub cmdExportReport_Click()
'Declare variables
Dim db As DAO.Database
Dim qdf As DAO.QueryDef
Dim varItem As Variant
Dim strCriteria As String
Dim strSQL As String
Dim NewDate As Date
'Get the database and stored query
Set db = CurrentDb()
Set qdf = db.QueryDefs("Query1")
strCriteria = Me!lstCFTs
NewDate = DateAdd("m", strCriteria, Date)
strSQL = "SELECT All_LastName, Mil_PRD FROM T01_StaffMembers WHERE Mil_PRD Is Null Or Mil_PRD Between #" & Date & "# And #" & NewDate & "#"
'Apply the new SQL statement to the query
qdf.SQL = strSQL
DoCmd.OpenQuery "Query1"
End Sub