Bot Problems

As a part time trader I am thinking that my time might best be spent designing a bot that can trade for me when I am at work. So currently I am in the process of trying to design one that will work on the Bet Angel Spreadsheet. I am making a bit of progress however my biggest problem is that I only want to trade in the last 5 mins of racing and then clear the status cells for the next race.

At the moment I have copied this bit of code from the Bet Angel forum and this clears the cells every time a bet is placed.

Private Sub Worksheet_Calculate()

Dim i As Integer
For i = 9 To 67 Step 2
If Range("O" & i).Value = "placed" Then _
Range("O" & i).ClearContents
Next i
End Sub

However at the moment this will fire too many bets into the market for me. So I am trying to write a macro that will clear the cells when cell I5 shows true. I have tried several things so far but they don't work in practice. I am sure it is possible so I will keep trying because if I can get this to work then I hope it will be profitable.