For general tips about speeding this up, see "Improve performance".
I'm guessing that the 20 lights might have something to do with increasing your render time.
That said, 20 hours is not unusual for a minute of HD material with a bunch of effects and blending and lights. I'm sure that the old-timers on this list would be happy to tell you about their weekend-long renders for SD material.
> Can I get a detailed log or something about what is rendered and how long it takes on a per-layer basis so I can see what is the bottleneck?
Thanks for this information.
Though partially misunderstood me, pherhaps I said it wrong. Sorry for that.
I am not having 20 lights. This is a relatively simple 2d composition. I added lightwrap: a copy of the background over the middle- and foreground with some glow and holdout to pretend the subject fits in better.
I do a lot of compositing, cg and rendering, and anyone in my shoes would agree one maybe two hours is a reasonable render time for what I am doing. The preview time remained the same or increased by a neglitable amount, but the final render time increased 10 times. That strikes me as odd to say the least.
I have to examine the More Information note from "Information shown for current renders" to see if I can get per-layer rendertimes but it is not mentioned. I will check that on my next render.
Do you use MP rendering? If so, you may have created yourself a pinch by using a specifc non-MP-safe effect or output format. In essence it would go into attempting to load certain things forever in the background, then fail (without proper warnings), only to attempt the same again after a few microseconds. If this goes on forever, the only remaining procerss that actually renders (the foreground instance), would also be impaired because it needs to throw a lot of resources on managing the badly behaving BG instances....