I bought this to be used on a motorbike. So does it need to complete a full lap to lock or does it lock once it detects movement?

Trying to get landscape locking to work. Holding my iphone4s in landscape orientation with laptimer open, swipe up and hit orientation lock button and the app immediately reverts to portrait mode even though I'm holding the phone in landscape. It stays locked in portrait mode fine however. iPhone4s ...