Msgs - Log entries emoved before 30 minutes 🔗 link

I am monitoring /var/log/messages for certain entries.  It seems to work
fine, except that entries on the msgs page are removed before 30
minutes.  They seem to only hang around for about 15 -20 minutes.  If
you click on full log, you only see entries that are less than about 20
minutes.  I thought they should be there for about 30 minutes.  Is this
configurable?  I don't see anywhere to change it.  I would like for them
to be visible for at least 30 minutes, longer if possible.