How to control VBA to only allow 1 instance of application.ontime to run

Question

I have a time loop using application.ontime which copy and paste blocks of cells from one workbook to another workbook every 5 minutes. From time to time it will copy and paste duplicates, making me suspect that there are multiple instances of it running. Is there a way to prevent multiple version of it running at once? Or is there a way to check how many instances of it is running (pending) at a particular time?

What I have so far in my application.ontime is the following:

Sub timer()

    If Hour(Time) <= 16 Or Hour(Time) >= 18 Then

        Application.OnTime TimeSerial(Hour(Time), Application.WorksheetFunction.Floor(Minute(Time), 5), 0) + TimeValue("00:05:00"), "dataextract", , True

    End If


End Sub

Secondary question: I don't particularly understand how it works in rich detail. Say I start an instance at 6:30pm... it works fine until 9pm and then I start getting duplicates. When I break the VBA, I get three pop up errors instead of one, confirming that there are multiple instances of it running. However I don't understand what could have caused it to duplicate? Could it be that I initiated application.ontime yesterday at 9pm and it restarted itself?

Answer 1

You could store the scheduled time and cancel the previous schedule before creating the next schedule task.

On Error Resume Next
Application.OnTime EarliestTime:=Range("NextSchedule"), Procedure:="dataextract", Schedule:=False
On Error GoTo 0

Range("NextSchedule") = TimeSerial(Hour(Now), Application.WorksheetFunction.Floor(Minute(Time), 5) + 5, 0)

Application.OnTime EarliestTime:=Range("NextSchedule"), Procedure:="dataextract", Schedule:=True