Use your own pace
Reading speed changes with text density, vocabulary, familiarity, font size and whether you are reading for enjoyment, detail or study. A personal pages-per-minute or minutes-per-page observation is more useful than a universal benchmark.
The Reading Time Calculator asks for your own pace. Time a normal sample rather than your fastest page, and include note-taking separately if it is part of the task.
Plan sessions, not only totals
A ten-hour book is easier to schedule as 30-minute or 45-minute sessions than as one total number. Divide the total by the days available, then check whether the resulting daily target fits your real schedule.
Leave some slack if the deadline matters. Missing one session should not automatically make every remaining day unrealistic.
Update after the first section
The first chapters provide better evidence than a guess made before opening the book. Recalculate after a representative sample if the original pace was noticeably wrong.