This (a goldilocks era) is a really interesting idea which seems obvious now that someone has brought it up. But it would be brief. Think of it this way, for millions of years the cosmic glow would be hot, too hot. Planets form, create magma oceans ... still too hot. Finally, the big bang glow cools to around 300K, but the Earth is likely still a magma ocean, or is still hot from trying to be in equilibrium with a hot universe plus internal heat from all those radioactives. Life aronse on Earth fairly rapidly, but it is unlikely that it took just a few million years. Even if it did arise on one of these worlds, it took billions for multicellularity to arise on Earth. After the brief goldilocks era what then? The sky would continue cooling, the worlds that were desirable places for new life would freeze, the ones that were too hot might now be suitable for life. In the end there would be little benefit. But there would still be planets around where life could start, though it might be complicated and very dangerous at this time.