So if I do a run can I prove what my time is by a picture in game of the save file after beating the game
We don't use save file time as our method of timing. I recommend using LiveSplit if you can, but any timer will do. Timer starts when you start your save file and ends when Kirby turns back to normal after the Mega Yin-Yarn fight. As for evidence, you always specifically need video evidence if your run is shorter than 1:50:00. Otherwise you don't need any proof.
Because it's faster to run the game with saves disabled, meaning that anyone using this strat wouldn't be able to see their in-game time. So, for consistency's sake, we don't time runs this way.
Wii Options > Data Management > Channels > Kirby's Epic Yarn > Erase However, I recommend keeping a copy of your save data on an SD Card so you can practice levels whenever you need to.
That's alright! You don't need to keep a copy of your save data, I just thought you might want to.
I don't have any save data that is important because I just run the game and delete any save files when I am done with them but I might still do runs with saving turned on because that is normal for me