To everyone trying to get the speedrun medal, your best bet is save scumming. Basically, it's saving at a statue, refreshing, checking the in game time of the save file then either copying it to another save file or overriding it with the other save file, of course you can't override your first every copy so if you are unsatisfied with that attempt, just delete and try again. And no refreshing isn't an alternative because you can't see the time taken of your attempt.
As to what time is considered satisfactory, just try to mimic this video as close as you can https://www.youtube.com/watch?v=J1Iusw8nUws but replace the timestamps in it to match
6:00, 18:11, 25:35, 33:38, 40:09, 48:50, 55:00, 61:00 . I use 61:00 as the final time just to be safe because the credits might take up to 3 minutes or something like that.
Using this method, the time taken to get the medal should be reduced to 1/10th of it's actual time, good luck because you'll need it.