With that said, Maderas is a wonderful cloud forest hike and worth the hike if you can afford the time to get to a trailhead! Contrary to what the tour guides say, the later the better; in the morning the volcano is covered in fog and it's not possible to see into the crater lake or out beyond the island. Book 6 hours if you're fast, 8-10 if you're not to climb to the top and back. Guides run $20/ea solo or split among groups of max. 3; book at any hotel.
For the record, if you decide to go to Maderas and need a place to stay, I would suggest avoiding Hacienda Merida; although it had good reviews in the Lonely Planet, I only found a profit-maximizing "resort" with truly horrendous customer service.
Isla de Ometepe from Lago de Nicaragua