It isn't exactly the same. It is correct that you can't use へ instead of に when it comes to times and dates like that. However think of へ as in direction and に for a specific destination.
So if you were headed in the direction of "wherever" but you might stop along the way somewhere, you could use へ. If you were specifically going to "wherever" you would use に. It's a very subtle difference but you can see where it's useful.
日本にいきます - I am going to Japan.
日本へいきます - I am headed to/towards Japan.