Wow! That's a good and hard question. From my experience it depends on the plant. For instance I have some Cuphea pods that were still green when pulled off (couple days ago). I noticed the seeds were still green inside and put them in a paper envelope. The pods continued to mature and the seeds turned brown. And seem to look viable to me. Also I have some Clematis integrifolia seeds which were picked and still green. I placed them in a paper bag and they have continued to mature and are now brown and the fuzzy tail developed.