Should we do this?
or this is enough
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If the duration is a year, nobody is going to track this for their own records and then keep you accountable if they are still logged in 1 year + 1 day from the initial login date. If you're set for 14 days or more, it might as well just say "Keep me signed in." save the characters, have less clutter.
However, a clarification on shorter time-spans such as "(for the rest of the day)" or "(24 hours)" might be noteworthy to the user. You can judge whether to use that by your user demographics.