In Link's case, as he is not yet Majora's Mask canon, he does not know how to use the Song of Time to reverse, slow, or speed up time. He only knows how to use it to manipulate objects marked with the symbol found on the door of time (giant blocks! yay!) to move them from one place to another - basically shifting them to a place they had been or will be in the past or future but making it manifest in that state in the present. This could >potentially extend to temporarily restoring broken buildings/large pieces of stone by shifting just them through time to points when they were whole and making that state manifest in the present. (thus potentially restoring a building like a hospital to working order for the duration of the event *if* and only *if* someone else gives Link the idea to do/try it - he's very linear and uncreative when it comes to his 'powers' since they're basically handed to him in canon).
The Sun's Song makes the Sun rise or set - depending on if it's played during the night or day - but in game it's not apparent if time is actually passing with it's being played. It likely is, because it wasn't used in Majora's Mask, so I can more than understand it not being allowed, but it was never explicitly made clear one way or the other in either game.
Re: FAQ
In Link's case, as he is not yet Majora's Mask canon, he does not know how to use the Song of Time to reverse, slow, or speed up time. He only knows how to use it to manipulate objects marked with the symbol found on the door of time (giant blocks! yay!) to move them from one place to another - basically shifting them to a place they had been or will be in the past or future but making it manifest in that state in the present. This could >potentially extend to temporarily restoring broken buildings/large pieces of stone by shifting just them through time to points when they were whole and making that state manifest in the present. (thus potentially restoring a building like a hospital to working order for the duration of the event *if* and only *if* someone else gives Link the idea to do/try it - he's very linear and uncreative when it comes to his 'powers' since they're basically handed to him in canon).
The Sun's Song makes the Sun rise or set - depending on if it's played during the night or day - but in game it's not apparent if time is actually passing with it's being played. It likely is, because it wasn't used in Majora's Mask, so I can more than understand it not being allowed, but it was never explicitly made clear one way or the other in either game.