You may mind map as you go or anytime you want to write a core idea. Some find it better to do mind mapping at the end which means you might need to glance back over the text to remind yourself of your finds. Sometimes it's easier to do one activation and then follow that with mind mapping with each activation.
The thing to remember if you're getting bogged down and writing too many words on your mind map; drop the pen. And get back to your questions. I drop the pen anyway even if I mind map as I go. It keeps me focused on getting down core ideas rather than copying the text.
Try it and see what works best for you.
AlexK