Not quite.
Prologue: 4+ days, 41 chapters
An unknown amount of time passes between Chapters 1 and 42. Sou is dreaming in Chapter 13, so that's presumably at least one night. Chapter 32 specifically mentions "the day after he wasn't allowed to go to an all-girls school," so that's another night confirmed. In Chapter 39, Sumire wonders why Akira suddenly shows up at the house a day after she sends her Sou's picture, confirming another day has passed. Those are really the only confirmed date transitions, which is at least 4 days, though most likely more than that. The exact timeline isn't really spelled out here. Having his hospital stay and release, re-integration into the household, spending time with his family, going to the sperm comprehensive center, and research, planning, and preparation for him to attend school all happen within 4 days really stretches suspension of disbelief even in a bonkers crazy series like this. (The main reason this portion is so comparatively short compared to his days at school is primarily because of the lack of perspectives involved and the escalating number of individual interactions and reactions at school.)
School Day #1: 1 day, 40 chapters
Sou's first day at school starts with Chapter 42 and runs until Chapter 81.
School Day #2: 1 day, 51 chapters
Sou's second day at school starts with Chapter 82 and runs until Chapter 132.
Holiday: 2(?) days, 11 chapters
Chapter 133 starts with the mention of "school holiday" which is presumably the weekend. (Miku also mentions getting through "the holidays" in Chapter 144.)
School Day #3: <1 day, 72 chapters and counting
Sou's third day at school starts with Chapter 144... and is still only half done by Chapter 215, so yeah, a really long 3rd day of school, but actually the 5th day (presumably) since he started school.
So he's been in this world for at least 9 confirmed days, but it's probably closer to 2 weeks by now, at least.