Tambunan city is about 2 hour journey from the Kota Kinabalu Inernational Airport. First go with the airport bus to Kota Kinabalu bus station (Rm5) before taking the minibus to Tambunan town. It cost about Rm20. There is no schedule you have to wait until the taxi is full. Usually they go until 2 pm or you charter the taxi for Rm72.