Estimate time for research on a topic.
Research time is reading time plus the surprisingly large cost of finding things. Searching databases, chasing citations, hitting paywalls and requesting inter-library loans typically adds twenty-five to forty percent on top of reading. Sizing the source count from research questions rather than guessing a total keeps the estimate honest, because each question needs its own body of evidence.
Reading volume
Sources = research questions x sources per question; reading minutes = sources x minutes per source
Search overhead
Total hours = reading minutes x (1 + search overhead) / 60
Learn the database query syntax properly, set up citation alerts, and use forward and backward citation chaining from a few key papers. Unstructured searching is the main source of wasted time.
Eight to fifteen for a coursework question, considerably more for a systematic review. The signal to stop is when new sources repeat what you already have.