Hi Aj, if your flight land in Kota Kinabalu then you can consider spending a day trip to Kinabalu Park the Mt.Kinabalu is located, a day at the beautiful island/beach by the city ( abt 15-30mins boat ride). Sapi Island known for best island for snorkeling, then there is Manukan Island, Mamutik Island. All beautiful beach. A day for garama river cruise where you will see the proboscis monkey by the river and evening cruise to see the fireflies. From Kota Kinabalu you may take early flight to sandakan where you can proceed to Turtle Island. If you have more time, you can take kinabatangan tour. if you are lucky you will see pygmy elephant.