Kindle's Time to Read estimates how long a chapter or book will take to finish. That estimate does not tell you the total time you already spent reading a completed title.
To answer that second question, you need a record of your sessions. Which record you can obtain depends on the Kindle model, software and profile you use.
What the time-left display means
Amazon's Kindle Paperwhite guide describes Time to Read as a prediction based on your reading speed. The available display and menu wording vary by model.
Open a book and look for Reading Progress or the progress display near the bottom. Where available, choose time left in the chapter or book. Give the device some reading before relying on a new estimate.
The estimate answers a planning question: can you finish this chapter before leaving? It does not give a session history. Subtracting today's estimate from yesterday's creates a misleading duration because the estimated pace can change.
Be precise about the profile you checked
Avoid a blanket claim that Kindle never records reading time. Amazon's older Paperwhite guide documents child-profile book statistics, including total time and average session duration.
That describes a particular mode on particular software. It does not establish the same display for an ordinary adult profile on a current Kindle.
Check your model's current guide and the screen available in your own profile. A streak, yearly book count or time-left estimate answers a different question from minutes spent on one title.
Record your sessions if you need a book total
A manual timer works with a stock Kindle and with print. Start it when you begin reading, pause for interruptions, and save the session against the book.
You can also keep a simple written log with a date, title and minutes. Add the minutes when you finish. Choose one method and use it consistently instead of combining estimates with timed sessions.
Suppose you record 25 minutes one evening and 40 the next. Your logged total is 65 minutes. Those are example entries, not measurements from a tested Kindle session.
If you forget a session, label a later estimate as an estimate. A rough recollection can help you remember your reading, but it cannot recover an exact duration.
KOReader can record activity on compatible devices
KOReader has reading statistics for activity inside its own reader. Its statistics use the settings you choose for time on a page. Screen activity remains a practical measure, rather than proof of uninterrupted attention.
On a compatible Kindle, installing KOReader requires a jailbreak first. This guide does not recommend changing firmware solely to obtain a timer. Check compatibility and installation requirements before deciding whether that setup suits you.
If you already use KOReader, the Seekquel add-on guide explains how its recorded activity reaches a reading log. It carries the statistics KOReader has recorded. It cannot backfill reading you did earlier in Kindle's stock software.
Match the file to the right book and verify a short session before relying on its total. A missing statistics record and a failed connection need different fixes.
Other reading apps need their own checks
Apple Books does track daily reading minutes through Reading Goals. Apple's support guide also describes yearly book and audiobook goals.
That is a daily habit measure. Check the app's own display before treating it as a finished title's total. The existence of one reading-time measure does not establish another.
This distinction applies whenever you compare apps. Ask whether the number measures remaining time, activity during a day, or recorded sessions for a book.
Pick the record you actually need
Use the Kindle estimate when you want to plan the next chapter. Use a timer or session log when you want to total time spent on a book.
Already reading in KOReader? Verify its statistics and connection instead of starting a second clock for the same session. The cross-device guide explains which connections carry duration and which carry position alone.