The modifiedTimeStamp attribute of an NodeEntry is currently being set when the eviction thread kicks in to valus Sys.CurrentTime (a). The inaccuracy is in the difference between (a) and the actual time when action took place, eviction event was created and added to the region(b).
E.g.
if we have a maxAge set to 15, wakeupInterval set to 10.
sec 0) node /a is added
sec 10) eviction thread kicks in, an NodeEntry is created with modifiedTimeStamp set to Sys.currentTime
sec 20) eviction thread kicks in again, notices that node /a is only 10 sec old and does not evict it
sec 30) eviction thread kicks in again and evicts node /a as it's timestamp is 20 sec old
In other words the node is evicted after 30secs. A better approach would be to pass the timestamp from eviction thread, which would reduce the inaccuracy and evict node in 20 secs.