I have been reading this for days already (Currently at chapter 57). It's pretty good considering the fact that this is a harem novel. Well, we all know that some harem novels focus on 'the' scenes without considering the plot. Here are just the first few things that I wanted to point out.
1. The MC may seem dense, but it's given since in his past life he was just focused on his studies without caring about the world. I just hope that he will be smart enough to fight Julius in the future.
2. The MC's power still has limitations so don't expect a very OP MC in the early chapters or else you'll get disappointed.
3. The Apocalypse that is mentioned in the story is still far since our MC went back 3 months before it.
I can say that the grammar of the story is good. It was just in the early chapters where there are minimal typos and mixed pronouns.
The MC is great and the girls too (I really love Abigail and Lilianne). His powers are interesting, although there were still left that are not revealed.