The DTIME column gives the time of the last detach from a shared memory segment.
Perhaps the entries that you are seeing simply have been created, attached but
a detach is yet to occur? If the segments are being created by the same application
it might just be a characteristic of the applications behaviour.
It's quite legitimate for an application to not detach for a long time. Of course, if the
application doesn't call shmdt it might be that DTIME isn't updated when the application
exits.
I would check which application(s) is creating the segments.
Regards,
Peter.