B+: Simple time-reminder without 100% CPU usage?

Hey guys. (problem stated after code bit..)

I'm trying to do a simple program, where you can enter a given number of minutes in a field. It will then remind you when that time is up. If you enter 1, it will remind you after 1 minute. Code:

MainWindow=CreateWindow ("Reminder",GraphicsWidth()/2-100,GraphicsHeight()/2-75,200,150,0,5)
Global MinField=CreateTextField (10,25,160,20,MainWindow)
Global GoButton=CreateButton ("Go !",10,55,60,20,MainWindow)

Global counter=0
Global target=0
Global MilTemp=0


Repeat
 eid=WaitEvent()
 Select eid
 Case $803
 Exit
 End Select

 If EventSource()=GoButton
  If EventID()=$401
   Go()
  End If
 End If
Forever


Function Go()
target=Int(TextFieldText(MinField))*60
MilTemp=MilliSecs()

Repeat
 If MilTemp<=(MilliSecs()-1000) Then
  MilTemp=MilliSecs()
  If counter=0 Then
   counter=1
  Else
   counter=counter+1
  End If
  If counter=target Then Notify "Time is up!" : Exit
 End If
Until KeyHit(1)
End Function

I'll facelift the program, when the code is okay. Here's my problem. While the time is running, I get 100% CPU usage. Isn't that a bit much? Is there some other way to do this, without that much CPU load?