I did use the book to establish routines once my baby was on formula at 4 weeks old. I don't think you can follow the book rigidly, it's just not practical, but I found it very useful to know when to drop a feed, and to be honest, my boy adapted to the routine himself. I was really lucky as he fitted the feeding times exactly, you could almost set your watch by it! He would down his feeds in one go with no fuss and then be happy to wait til the next one. This is probably easier when you're using formula as it fills them up more than breastmilk. But I know it doesn't suit all babies, some babies prefer to 'graze' with their milk, taking a little at a time. A friend of mine was told by a mw that if you are the type of person that snacks ('grazes') throughout the day, then it's quite likely that your baby will have similar tendencies.
One thing I ignored in the book was to wake my baby from his nap after the 'allotted' time! Let them sleep if they need it, they'll only be grouchy if you wake them up!!
I also used the Gina Ford Weaning book which I found quite good to introduce all the different veg if you haven't done it before, as I didn't know where to start!
Anyway, there's no set way to do things, do what you feel comfortable with and what suits your lifestyle. I used the book as really I didn't have a clue where to start! I have to say though, I don't know if it's got anything to do with using the book, or just his personality, but my boy is very calm and laid-back - long may it last!!