Summer Time Render has its own unique premise in the manipulation of time, which is one of the most fascinating theme that would surely leave the readers wanting more after every chapter. It's a perfect manga to binge read, though I can imagine the pain of waiting for more chapters during its still releasing days.
Character development in this manga is especially great. Almost all characters have their own story to tell, whether big or small. And it's not detrimental to the story at all because the development is organic and well connected.
The story, well, for lending the vast power of time manipulation in telling, may arguably have some plot points. I even sometimes wonder, "Huh, how did this happen?" and "How is it possible here?". However, the manga still has an ending that could satisfy most readers.
The only issue I have for this manga is that, the number of pages varies greatly between chapters. The short chapters would definitely frustrate avid readers as they left the story at a cliff hanger many times.
Final thought: Whether or not your preference is time manipulation theme, everyone should read this manga once. Or, at the time of this comment, the anime has reached around half of its runtime, and so far, it's adapting quite fatefully. So you can opt for that to explore this story. Maybe I will edit this comment to give my thoughts on the anime too after seeing its finale.