It depends on how well you are focusing on that particular textbook.

If a textbook has a lot of dry, dense material and you have trouble focusing, I think taking a break between sections is helpful. I'd say taking a break for about 5 minutes to get up, stretch your neck, look outside, take the garbage out, go check the mail, put the dishes away, etc. is good. If the material is engaging, try to read it straight through.

Right now I am taking a class where the text is an awful, dry read and it's dense. I often have to consult youtube to see a visual explanation. However, because of how awful the text is, I read straight through. Then I re-read and highlight. Then I take a break, and skim through and take notes of what I highlighted. No, I don't do this for every class. This class needs it because it's the only way I seem to digest the material.

There's another class where I can read the chapter and understand it immediately. It's easier to read all the way through, and a break is only needed because of how long it took me to read.