Mark Articles older than X as read
Basically this is identical to what Google Reader had. It had options like 1 week, 1 month, 6 months, etc, it will take all those articles older than the specified period and mark them as unread, but also marks the articles newer than that period as unread.
Great for reversing accidental "Mark all as read".

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imutau commented
As fast as some of these articles become old news especially if you have "deal" feeds it would be even greater if we could one up Google and have options like older than 8 hours or older than 1 hour.
Even better if these could be set per feed and not all feeds. So we could have different "mark as read" time frames for each feed.
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ToniCipriani commented
Sorry I meant "older than the specified period and mark them as read", and newer than as read.