At our public Montessori, the prek/K classes are 3 hour days, so a 3 hour cycle just isn't possible. And they have to provide lunch during that time, too. If the K students want to eat lunch at school, they at least get there before school starts so they have more work time in the classroom. But then the K students have to go elsewhere for PE and music, so they do get interrupted. The Montessori school is housed with a traditional school, so they share the extra curricular teachers.
However, the teachers are aware of this, and they do try their best to have as much uninterrupted work time as possible, for instance scheduling extra curriculars for a time that is not right in the middle of a work period. And when they do work, the students are able to choose what they want, and there certainly aren't scheduled "subject" times. All the teachers I've talked to at the various grade levels have been pretty up-front about modifications they've had to make in order to accommodate state standards, and I'm confident they do it in a way that is as "Montessori-ish" as possible.
State standards are usually specific about "what" has to be taught... but not "how" or what kind of schedule there needs to be.
Melissa , wife to Tom , mom to The Baron , the Bean , Little Bear , and Baby Beaver