If someone asks how relations can improve when the bar is at the bottom:
I maxed out my relationship with Rosalina without any romance. The progress bar got stuck just one pixel away from her giving me the house key, and it stopped increasing with each new day.
Then she invited me to the baths. Right there in the baths, romantic feelings formed, and the maximum relationship cap instantly increased without waiting for a new day.
So the game already has a mechanic that allows raising the current relationship limit without needing a new day. The same thing could work with Acacia.