Ah, you must be a planner mom!
I am one of those too, so I recognize a fellow planner!
The transition is pretty organic, actually. Especially with a textbook! What usually happens is they just start extending their A times. Up to 6 months old, babies typically need to increase A times by about 15 minutes every 4 weeks. You can tell when they need to increase As because naps begin to get shorter. Sometimes rather suddenly -- one day you have a 2 hour nap, and then the next day it's 30 min! So you increase A times which puts your feeds a little farther apart. You may also notice that some of her feeds are smaller than others -- for example, she'll have a 2 oz feed followed by a 6 oz. That means she wasn't quite hungry enough for that 2 oz, and then she made it up at the 6 oz feed. This is why it's important to always try to have an oz left over in the bottle at the end of each feed -- you want to always offer more than you think she will take. If you BF, then she'll simply feed shorter than normal, and then longer at next feed. No need to adjust anything!
Most problems at this age actually stem from a developmental shift that occurs around 12 weeks old in the REM/non-REM pattern. That often causes short-napping (45 min) and really messes up routines. That isn't related to the change to a 4 hour EASY at all, but because each baby reaches this developmental milestone at different times, some moms have the bad luck to have a baby going thru the short-napping phase at the same time baby is ready to move to a 3.5-4 hour EASY. So it can get very confusing! But really, if you treat the developmental short nap as a separate issue, once its sorted out you should slowly be able to enter the 4 hour EASY without too much trouble.
