Convert ISO8601 Dates to Excel Date (Variant)

iso8601todate

Public Function iso8601todate(iso As String)
    Dim result As Date: result = DateValue(Mid(iso, 1, 10)) + TimeValue(Mid(iso, 12, 8))
    Dim signPos As Integer: signPos = InStr(iso, "Z")
    If signPos = 0 Then signPos = InStr(iso, "+")
    If signPos = 0 Then signPos = InStr(InStr(iso, "T"), iso, "-")
        
    If signPos <> 0 Then
        Dim zone As String: zone = Mid(iso, signPos)
        Dim sign As String: sign = Left(zone, 1)
        If sign <> "" And sign <> "Z" Then
            Dim timeDiff As Date: timeDiff = TimeValue(Mid(zone, 2, 5))
            If sign = "+" Then
                result = result + timeDiff
            Else
                result = result - timeDiff
            End If
        End If
    End If
    iso8601todate = result
End Function

Use normal Excel cell formatting to display the resulting date.