This is probably more Openfire issue, because Openfire is not showing last logout value for the most of my users. Dont know why yet. But for such users Spark is showing "Idle for < 1 min". This means less than a min. Which is wrong. I think in scuh cases, when there is no info in server's DB it should show some message like "Activity info unavailable" or like that.

Related thread in Openfire support:

http://www.igniterealtime.org/community/thread/29394

SPARK-942