Breadcrumbs - to answer your question, all the books I've indexed so far have been between 35 and 75 recipes. The first one took the longest since I was taking a lot of time to study the manual and make sure I was filling out all the sections properly.
Once I got the hang of it, I usually could index a whole book in an evening or two after work, depending on how much I felt like doing at once. Most times I'd do the indexing and then take a break and proofread/edit my work in another "session" so to speak, so I'd be looking at it with fresh eyes. Another thing that helped the indexing move quickly was that most of the books I did were single subject so a lot of the category, nutrition, recipe type, occasion, and course information was the same for most, if not all of the recipes in that particular book. All that being said, if pressed, I would say that if I were focused only on indexing and not jumping up to do laundry or some other household job, I probably could finish a 75 recipe book in maybe 2 hours.
The more I index, the easier and quicker it seems to get. I have to admit that I initially thought I'd only index a book or two, but I've really enjoyed doing the indexing and also really like the idea of having a more complete catalog on EYB, so in a short time, I've already indexed 7 of my books! I'd suggest trying it and seeing for yourself how you like it. Hope this helps!