What minute and second was supose to be the end of act 1? Dont recall:S
Around 1:15 is when it starts to look different to me. Maybe a little after. Basically when he does that big jump and gets all those rings in the air.
Just did a quick run through of Act 1 on my 3DS and there is a tiny bit more to the original stage after that jump but the jump basically is the end of the level.