VBA to skip if certain cell is blank

Hello,

I have the current code but I need it to skip certain rows if column "F" contains a date. I would assume this to be fairly easy to add to the code? I've attached a sample spreadsheet to help. All help is most appreciated!

PHP Code: 

Sub ChangeLetterCodesByRowMG()

Dim Col As Long
Dim Letters As String, NextLtr As Long
Dim NextA As Range, FirstA As Range

Application.ScreenUpdating = False
Letters = "BCDEFGHIJKLMNOPQRSTUVWXYZBCDEFGHIJKLMNOPQRSTUVWXYZ"
Set NextA = Range("T:X").Find("A", LookIn:=xlValues, LookAt:=xlWhole, _
                SearchOrder:=xlByRows, SearchDirection:=xlNext)
Set FirstA = NextA

Do
    If Rows(NextA.Row).Hidden = False Then
        NextLtr = InStr(Letters, Cells(NextA.Row, 24)) + 1
        For Col = NextA.Column + 1 To 24
            Cells(NextA.Row, Col) = Mid(Letters, NextLtr, 1)
            NextLtr = NextLtr + 1
        Next Col
    End If
    Set NextA = Range("T:X").FindNext(NextA)
Loop Until NextA.Address = FirstA.Address

Application.ScreenUpdating = True

End Sub