I apologize for such a short reply earlier, but just as I was thinking and trying to post, the phone rang and dd started to wake from her nap.
Anyway...It is totally okay to have different amounts of time between each feed. For example, some can be spaced 3.5 hrs and others 4hrs. I understand that the example in the book is confusing, but the general idea I think is to eventually consolidate the 1 and 4 o'clock feeds into one feed at 3. It is fine to just take the plunge if you think your dd can handle it. Mine just slept past a feed one day and we never looked back.
You can certainly keep the same df time through all of this. And you can still feed at 7, even if she doesn't take as much, she might make it up with the df.
Here's some examples:
7, 10:30, 1:30, 4:30, 7:30
7, 11, 2:30, 6:30
7, 10:30, 2:45, 6:45