When we talk about self publishing , it means a collection of services like cover design, layout (interior of book), Editing, print publishing (Hardcover / Paperback), E book and promotion of the book. If it a Children’ book , then illustrations also play a very important part.
When we talk about various services, the next thing is the length of the book in terms of number of words. This directly impacts the number of pages which impacts the editing and layout and of course the print cost.
So, for most of the books the time frame for Self publishing is in the range of 5 weeks to 8 weeks. In case of Children’s book , the time frame will increase specially because of the illustrations. The range may be between 10 weeks to 14 weeks for a standard Children’s book (with 12 illustrations and 30 pages).
Having a professionally designed cover is very important because the cover is the first impression for the readers and if its not good, there are minor chances of your book doing well. Even if your story is excellent but if the cover is not designed well, the book has low chances of doing well.
I always recommend that the authors must be ready to give extra time when the cover is being designed. Don’t mind a few extra round of revisions and ask your designer also to keep more patience. The cover must be shown to a few other professional designer and author friends to get the correct feedback . o hurry should be practices when it comes to cover.
As far as the layout and editing is concerned, if you choose a professional agency, they should do a good job. But be careful to do one round pf proofreading yourself or choose random pages and just do some proofreading.
When it comes to book promotion, this is an activity which is not included in publishing time frame, it start after the book is published and I suggest that it is an ongoing process and author must develop an online presence for himself.