Task 1: To the Grove
A Golden Bird
After your victory against Blizzeta, head back to Telma's bar. She'll direct you to North Faron Woods, where Rusl waits for you. Leave the bar and warp there, then turn back into human and talk to Rusl. He explains that an ancient temple on the other side of the gorge holds a secret, and he'll give you the necessary transportation to get there: a golden Cucco.
Pick up the bird and use it to glide straight across a gap to a ledge. Turn and glide to a root that juts out from the cliff, then turn again and glide to another ledge. From there, manipulate a few bridges with the Gale Boomerang, then glide some more into the Sacred Woods.
The Skull Kid
On your way to the temple, you'll run into Skull Kid and his skeletal followers again, this time in human form. Defeat the followers like before, then search the woods for the ringleader. You'll know you're close when the music gets stronger and you see lamplight (you have to be real close to him to notice the change in music volume). After finding Skull Kid, hit him with your sword or arrows. When you've hit him a total of three times, he'll lead you to another arena. Clear away his followers, then hit him with an arrow three times to gain access to Sacred Grove.
Task 2: Entering the Temple
A Link to the Past
When you enter the grove, push a large block to clear your way, and head over to where you retrieved the Master Sword. By returning the Master Sword to the pedestal, you'll cause a statue guarding a doorway to disappear. As you head over to it, five shadow beings drop from the sky. Defeat them either as a wolf or in human form, remembering to defeat the last two at once. After the battle, head over to the unguarded door and enter it. You'll go back in time to the days when the Temple of Time stood fully intact in all its glory.
Window of Illusion
In the temple, head to the chamber of the sword and plant the Master Sword in its pedestal to cause a luminescent stairway to appear. Head up the stairway and through the fake window to enter the Temple of Time.