I am getting a DVR recorder installed. Never had one so my question is... how much can I record on a DVD? Say I set it to record a hour show on TNT and I want another show that is later the same day on another channel. Can this be done or do I have to be here to insert another DVD?

We have done a lot of dvd taping and all out disks have been six hours. The label on the new dvd packages list the length.
When you put the disk in the recorder, after it loads, the menu screen should come up and show a space of 6 hours available. Make sure you are set on the right speed which would probably be extended play. Speed is changed on our machine with a "rec mode" button on the remote and is done while still in the menu screen.
It should change channels with no action by who later on. But read the manual, there are a lot of different features. Finalizing is one of them.