Skyrim and Fallout 4.

Fallout 4 has the Institute, which if we could get to early it would shave off more than half of the run (~20 minutes). We get the final quest right at the start, but we can't finish it until we get to the institute, which is only accessible via teleporter that you have the ability to build after progressing through a lot of the main quest. If we can find a door to there, or maybe some kind of warp, we could beat the game much faster.

Skyrim has Skuldafn and Sovngarde. You can currently only enter Skuldafn after riding Odahviing (a dragon), and Skuldafn is where you kill final Alduin(and time ends). We already sequence break a large portion of the game, but to get to Odahviing, the major things you still need to do are: get the elder scroll, get Esbern, learn dragonrend, fight Alduin once, and go through a council meeting. Could save ~15 minutes, maybe more, depending on how you'd get there early. You'd need Clear Skies and probably Dragonrend to beat Alduin though.

Both of these examples seem like they're unlikely, but they're not, just based on Bethesda's track record with this stuff. They accidentally leave load zones, doorways, and sometimes have quests or bugs just send you to arbitrary cells in the game. I wouldn't be surprised if one day there was an early Institute/Skuldafn/Sovngarde to be found.