The answer is simple. Use the "Tag" property to store the time you want the timer to go off. Then do a test to determine if it has elapsed or not

Code:
tmTimer.Interval = 1000
tmTimer.Tag = dateadd("s",120,now())
tmTimer.Enabled

Public Sub tmTimer_Interval()

  If datediff("s",now(),datevalue(tmTimer.Tag)) <= 0 Then
    tmTimer.Tag = dateadd("s",120,now())

    ' Do your code here
  End if
End Sub
I haven't tested the code but thats the general gist