Estimate time for an annotated bibliography.
An annotated bibliography is dominated by reading, not writing, and that is the reason students misjudge it so badly. Fifteen sources at eighteen pages each is 270 pages of academic text, which at a realistic 12 pages an hour is over twenty hours before a single annotation is drafted. Academic reading speed is far below leisure reading because you are extracting argument and method rather than following a narrative. The annotations themselves are quick by comparison, and citation formatting adds a small but real overhead per source for chasing DOIs, page ranges and inconsistent metadata.
Reading time
Hours = sources x pages per source / reading speed pages per hour
Total time
Total = reading hours + (sources x annotation words / writing speed) + sources x 6 min citation work
Because you cannot annotate what you have not understood. Academic reading at 10 to 15 pages an hour is normal when you are identifying the research question, method and limitations. A 150-word annotation takes under an hour to write but the twenty pages behind it take considerably longer.
Partly. Reading the abstract, introduction, method summary and conclusion first often gives you 80 percent of what an annotation needs, and lets you decide whether the full text is worth reading. That can double your effective pages per hour without weakening the annotation.