This... this is true. It's a large Guay (probably about two times larger than usual). If you look towards Ikana and look up towards the mountains, one comes out. Like she said, it drops one red rupee. If you look towards Woodfall, another one comes out that is the same size. However, unlike what she said, it does drop a red rupee (it's just too close to the telescope for you to see it drop one). I do not believe that the time of day matters. Once you go out to Termina Field, you can collect both red rupees. Wow... I never knew about this before, though (and I know a lot about this game).

Edit: Err, my bad.