VBA Code To Sort Data - Run-time Error When No Data To Sort

I havet he following code which sorts data. If there is no data to sort I keep on getting a run time error. Could I add something to my code to prevent the run-time error, as sometime there won't be any data to sort. The code runs when I switch to the worksheet in question.

Sub SortMeetings()
Dim iCTR As Integer
Dim yCTR As Integer
Dim zCTR As Integer

zCTR = 11
For iCTR = 12 To 23
For yCTR = 1 To 10
If Len(Range("D" & iCTR).Offset(0, yCTR)) 0 Then
Range("AA" & zCTR).Value = Format(Range("D" & iCTR).Offset(0, yCTR), "HH:MM") & " " & Range("D" & iCTR).Value
zCTR = zCTR + 1
End If
Next yCTR
Next iCTR
Range("AA11:AA" & zCTR).Select
Selection.Sort Key1:=Range("AA11"), Order1:=xlAscending, Header:=xlGuess, _
OrderCustom:=1, MatchCase:=False, Orientation:=xlTopToBottom, _
DataOption1:=xlSortNormal
End Sub