Being able to access the Snowpeak Ruins early can be crucially helpful in the game, especially since half of the dungeon is already skipped in an Any% by accessing the City in the Sky Early. Having early access to the Ball & Chain also opens up new strategies that can be used to defeat enemies and Mini-Bosses much faster than usual.
After the Lanayru Twilight is cleared, the ice door blocking access to the Peak Province is no longer there. (This wall can also be bypassed using cutscene diving if you have the Master Sword Early while still in the Lanayru Twilight.)
However, you will find if you try and access the Snowpeak before due time, even if you know the route without the Reekfish Scent, you will get lost in the snow storm and be transported back to where you began.
In order to overcome the snow storm, perform Map Glitch upon entering the Peak Province from Zora's Domain.
This will prevent you from getting lost in the storm, which then allows for early access to the Snowpeak Ruins.
It is very important, however, to remember to howl at the howling stone before you use the dig spot into the cave (to disable Map Glitch), or else your game will freeze.
With a very precise position and good luck, you can superjump off a Wolfos to reach the upper cliff, bypassing the reekfish trigger and allowing you to do early snowpeak without map glitch.
It is possible to to get Snowpeak even earlier than Post-Lanayru Twilight which before Lanayru Twilight but after thawing the ice which means completing Eldin is still required. There are two methods of doing this, one utilizes a Rupee Dive and requires Barnes’ Bomb Bag and Fixed EMS, while the other method doesn’t require anything special apart from some tight LJA and movement. Unfortunately this is slower for any speedruns due to the fact it requires beating Eldin Twilight first anyway for thawing the ice.
This requires Fixed EMS for Barnes’s Bomb Bag and a rupee dive. Once the ice is thawing you need to be on the land on the right side, from here use your bombs on the rocks blocking the path to reveal a blue and yellow rupee which will not despawn and can be used to setup the Rupee Dive. Use the box to push the rupee to the edge of the land, when ready do the Rupee Dive, wait half a second after you can close the textbox then close the text to stop the dive, from here you can swim up towards the Snowpeak Mountain exit, if you start getting carried away by the water current towards in bounds you can use the boots to sink again and control yourself, once behind the ice wall the current can clip you back in bound and allow you to enter Snowpeak Mountain.
This requires nothing more than precise movement and LJAs. Start off by doing Map Glitch to disable all loading zones, from here go through the loading zone to Inner Zora’s Domain on the right side and rub against the wall while slowing going back, once you fall off the ground you can Jump Attack to clip back up and recoil off the wall, if done right Link will be grabbing the edge of the ground through the fall and you can start to slowly climb sideways towards the main area. Once you have gone far enough you can climb up onto some ground that is behind the wall OoB, from here it is possible to LJA into the water. It is now possible to go around the edge of the map towards the Snowpeak exit, using Iron boots when required to regain control and then clip in bounds behind the ice wall using the current. However because Map Glitch was used to get behind the loading zone at the top there is no way to enter Snowpeak Mountain, luckily there is a savewarp trigger in the tunnel that once walked over you can savewarp to reappear behind the ice wall but now with all loading zone active.
It is possible to reach Snowpeak province before melting the ice in Zora's Domain, allowing you to reach Snowpeak Ruins without ever getting to Kakariko Village. To do this, first you must activate map glitch to avoid a crush void later on. Then, use the boomerang to grab a Keese from the top of the waterfall in outside Zora's Domain, and with an LJA to the out of bounds cliff, navigate with the Keese to a ledge just above the lower tunnel area. Throw the boomerang + Keese out so that it will follow you, then sidehop down left to land in the lower tunnel. Bring the Keese up to the rock blocking the shortcut, then perform a Superjump off of it so that you land on top of the rock. From here, with a precise position and angle, you can backflip to the right-side portion of the rock and slide off of it. With two frame-perfect jumpslashes, Link will land on a lower portion of the rock, allowing you to move for a moment before slipping off. From here you can perform a backflip, and with a good angle, you will clip out of bounds beside the rock. Equip Iron Boots mid-backflip to land on top of the rock in the out of bounds area. Lastly, perform an LJA from on top of the rock to land down in the cave leading to Snowpeak. Because map glitch is activated, the loading zone is deactivated, but you can touch the back wall and savewarp to set your save location. After reloading your save, you can enter Snowpeak normally and continue as usual.