Potentially obvious questions

I'm farming materials in Duviri and I have 2 questions I'm curious about.

First, I know decrees are what saves the resources obtained before leaving, but is it when you GET a decree, or is it when you make the choice for a specific one? Can I pocket a decree, do my farming then just pick it?

Other question, if I go around the open world and grab what I need, does progressing into a Warframe section and coming back out refresh the materials around the world, or do I need to quit the run and restart?