Hi sineadW <–you’ve been camel-cased
I started the book Sept of last year and finished it Jan this year, however, I did have about a month worth of work travel and no study so, in all I’d say it took me 3-4 months at a slow-moderate pace. My objective going into this was to master Objective-C as much as possible before diving into Cocoa and Cocoa touch development so I took my time with the chapters, I didnt just set out to finish the book fast, in fact, I sat and pondered what I learned on some of the chapters for a week or two in some cases to make sure I fully understood the concepts (sometimes advancing one or two chapters makes the previous one click - everybody’s learning style is different). I also read and experimented with the various classes using the Apple reference and guides, as a way to supplement the content as I went through the chapters. The book to me is just one more tool (a very good one at that), not just a means to an end.
As for previous C experience, not very much. I took C in college ages ago and do understand programming concepts but that’s the extent of it. I think the Obj-C book covers enough C to get you started, and as you will find as you progress through the book and learn the Foundation framework, you will continue to touch on C on/off since ObjC is just a superset of C and you will still rely on C types, structures, C-arrays, C functions, etc to accomplish many tasks (by the way, this continues on even on the iOS book - CoreGraphics for example, is a C based API and you use the API directly to accomplish a lot of stuff that hasnt been abstracted one layer up yet). lastly, remember the C is a procedural language so spending too much time on a C book may not help further your thinking in terms of classes and objects, which is where you really need to be in this context.
Stick with it and have fun!