Has it been changed as a 5th edition thing that any potion lasts a long time? In my past experience there's never been a potion that lasts long. It simply was never a thing that I recall. Potions aren't supposed to last all day. Not any potion that I've ever known of in past editions.
On a side note, if you use a potion of resistance of any kind it over rides the hill giant strength but I think those are the only potions that effect it. Haste, invisibility, healing, those can be used fine.
