Copy to Visible cells after filter

Your recorded code will need editing to something like this. I have assumed the header row is Row 1.

OptionOption Explicit

Sub AddFormula_FiltereRange()
    Const sCrit As String = "a"    '<- change date here
    Dim FilterData As Range
    Dim OldValue As String
    On Error GoTo exit_handler
    With ActiveSheet
        If .AutoFilterMode = False Then .Cells(1, 1).AutoFilter
        .Range("A1").AutoFilter Field:=4, Criteria1:="=" & sCrit
        ' On Error GoTo exit_handler
        Set FilterData = .Range("A1").CurrentRegion
        With FilterData
            OldValue = .Cells(1, 7).Value
            .Offset(1, 0).Resize(.Rows.Count - 1, _
                                 .Columns.Count).SpecialCells(xlCellTypeVisible).Select
            .Columns(7).Formula = "=5*5"
            .Cells(1, 7).Value = OldValue
        End With
exit_handler:
        .AutoFilterMode = False
    End With
    On Error GoTo 0
End Sub