Yastian still sells potions past 5 PM and I think it's a bit misleading, not to mention a bit arbitrary. The potion effect should last hours after taking, not just until a specified time at night. I just watched six people all have the same experience of buying several elixirs because the effect would not stick, to then run to the mist wall at 5 PM and be kicked out despite overdosing on the elixir.
I truly wish this mechanic would just go away.