Finalizing Time

I have a Panasonic DMR-EH50 and I often record films from TV then dub them onto a DVD-R using Flexible Recording.

One thing that puzzles me is the very large spread of time that Finalizing takes. It is often only a minute or so but, not infrequently, it drags on and on to over 5 minutes and, occasionally, it refuses to finalize at all.

Why is this? Is it because I am using FR which, presumably, means that there is very little space left to accommodate the finalizing? If the film was a few minutes under 2 hours would I be better off using SP - I’d guess that the loss in quality would be minimal. Or what?