How did you establish that it's taking 80 hours? Is that just some estimation when you start encoding and then you abort the process, or did you actually wait and successfully encode a project within the time frame of 80 hours?
80 hours sound extreme, but while I have never seen the time estimation being off that much, it might just be the case here. Something in the project that is temporarily slowing down the encoding a lot might totally throw off the estimation. If that doesn't seem to be the case, more information about your source material and project might be interesting.
If it's really just a total of 1 hour video and you haven't done anything extremely weird with the menus either, you should easily be able to fit it onto one single layer DVD and still get a decent quality bit rate. Any chance you have cranked up the MPEG encoder bit rate to the highest value and possibly also included a rather extensive menu (long background songs/videos etc.)? In this case, you might really break the 5 GB limit for one hour of main movie. So, check for these things and make sure the MPEG-2 encoder bitrate (which you can access from the burning dialog) is at a reasonable value. Somewhere between 6000 and 7000 kbps are the default value and should be sufficient.
See what you can do to break the project down into more managable 'bite size' chunks.
If you know the final format - for each 'movie' - export it to that 'final format'.
Then, when building the DVD, bring all these bits and pieces - already in the right format - into a NEW project.
Then when the DVD burns - it does not have to reformat everything for the final output.
I'm working on a long DVD too - it'll be about 90 minutes when I'm done. It is taking numerous projects in Video Edit - what? - maybe 25 projects now - and one final project just to build the DVD.