My middle school had 48 minute blocks like this. 7 per day, if my memory serves, with 3 minutes between periods to change classes and I don't remember exactly how lunch worked.
My high school had four 90-minute blocks. 7 minutes between. 3rd period was actually 2 hours, and you'd have one of four half-hour lunches (so, sometimes 90-30 and sometimes 60-30-30, and each of those reversed).
I hated the middle school setup, in which settling down took the first 15 minutes and the last 10 were spent packing up (since the time between was so short, you had to be packed when the bell rang). High school was so much better... but my brother hated it, because focusing on the same topic for 90 minutes straight with no breaks was difficult. (And it made scheduling difficult, but that's tangential here).
So I think the moral of the story is that there's no silver bullet, and breaks are important, even if you don't change topics.