Conditional formatting can be apply to entire cell. There is no such function to apply to characters which is after 12 lengths.
If you don't want to use macro, you may try formula to divide the cell into 2 parts.
=LEFT(A2,10)
.
=MID(A2,11,1000)
.
Here is the step for macro, you may have a try.
Alt+F11 to open VB Editor, Paste code in it. Then press F5 to run the code.
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Sub RedCharacters()
Dim cell As Range
For Each cell In Range("A:A")
If Len(cell.Value) > 11 Then
For i = 11 To Len(cell.Value)
If Mid(cell.Value, i, 1) <> " " Then
cell.Characters(i, 1).Font.Color = vbRed
End If
Next i
End If
Next cell
End Sub
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