Time on Frog Island

This achievement is for sleeping at all 3 of the campsites in the game. To sleep at a campsite, you need to put 3 pieces of wood in the fire pit to automatically start a fire. The three fire pits always have 3 pieces of wood lying around, though the boat fire pit sometimes only has two, but you can use driftwood from the beach nearby as your third.

The first is fairly obvious; its right where you wake up by your beached boat.

The second is almost straight East from your boat after crossing two small rivers and following the Beach further. You'll see a fire pit next to a Bench.

The third is slightly up the mountain behind the Village, near what I assume is the Hermit's House. Follow the path up the mountain but take a bridge West on your way up instead of going North further up an incline. Near this building is the third and final campsite. Once you have slept at all 3 on the same save file, the Achievement will unlock.