When I do my typical playthrough I get it between the Forest & Fire Temple (which is the point you're at). It's kinda ideal to get it then since the side quest ends at the top of Death Mountain which is right by the Fire Temple. If you're gonna get it before doing the Ice Cavern/Water Temple it's a good idea to buy a bottle of Blue Fire, as you need it for one of the trading sequences. The fire costs 300 rupees at the Kakariko shop so you'll need the Giants' Wallet. You can always go to the Ice Cavern and get blue fire for free, but for me it's well worth spending the 300 to not to go out of the way to get it there. Plus, I buy it before the Forest Temple, so I earn a lot of the 300 back thanks to the Wallmasters. Even still, from where you're at in the game you'll make the 300 back before you know it .. and you really aren't gonna be spending any money on anything anyway, at least not until probably near the end.