I have some questions regarding mindmapping technical books mostly....

1.Can i mindmap just after 20 minute activation or do i have to wait a bit?
2.Should i mindmap information from my memory or should i copy from the text directly looking through them? What i mean by this is after few 20 minute activation do i have to close the book and fill the mindmap from whatever pops up in my mind or i can simply just look through the book and fill the map?
3.What are some efficient or recommended way to activate and mindmap?

Thank you