It's simply not possible. There's been done many experiments on exactly this subject, and it always results in the same thing: Time can't be altered. Not even in dreams. You might remember a dream like, if it was 5 days long, but that doesn't necessarily mean, that you remember every single moment. You just remember it like "Around that time of the day, I did that, and at that time, I did that and that".

If it happened, that you were stuck in your dream for such a long time, your instinct of survival would just wake you up. Or you'd find a way, to change time back. Otherwise, you'll go insane. Or have a good time.