Then you waste more of what precious little time you have and the dungeons are still tediously long with gimmicks that outstay their welcome. Better to be done with it in one go.
But it's not "little time" though. It's only little time if you try to do every single thing in the game in your first playthrough itself. You think the game was designed with that in mind?
That sort of completionist mentality is what gets you bored and makes you feel like the game feels like a drag because you are ticking off checklists for each day instead of playing it as you go. And you do that to yourself. Majority of the players won't be so strict about their timing, and for them the dungeons will feel perfect length for the most part. Making it shorter will make it feel right length for people who want to micromanage every day of the calender, but it will in turn make the dungeons feel awfully short and incomplete to the other group of players.
Just for reference I was very relaxed on my first playthrough and I had an amazing time, by the time I started NG+ I could do things even faster because I was OP from the get go plus I didn't have to spend any time building up my social stats meaning even in NG+ I don't have to micromanage things. Infact I am pretty sure I will have absolutely nothing to do for the last month in NG+.
Tldr: There is plenty of time just keep your completionist run for NG+. Infact if you want to be a completionist then you have to do a 2nd playthrough since some things are NG+ exclusive. Meaning all that acute time management in first run becomes useless as you get so much more time in 2nd to do stuff.