There's a chest with a Silver Rupee (100 rupees) in East clock town, go near the observatory entrance, follow the path to the right you'll see a small gap that you gotta jump across, keep following that path (past the Darling and Honey shop) and you'll get to it, good this is it resets each time you go back in time, so you can farm rupees there easilly.
There's also a second chest when you get past the bomber kid blocking your way (area leading to the observatory). Once you get past the kid instead of going right, go left, there's a bit of water and a small place you can stand (past the skulltula), you'll see a cracked wall, blow it up with a bomb and the chest in there has another silver rupee.