You have 6 in-game hours to save the frog before it's too late. If you rest at an inn, it'll speed up the time the frog gets digested by one in-game hour. You'll have to continue up north until you find the cove. Then you'll have to complete some puzzles until meet up with the shark. Click here for a walk-though document made by the developer for more information on how to save the frog.
However, it's IMPORTANT to know that if you're doing the vore route, then no matter what, you can't save the frog.