How much time does it take to journal? I think it would depend on whether you start or end the day journaling. I can see how starting the day with a journal would be good for productivity. You set you intentions in advance of the busyness of the day.
I can also see how ending the day journaling would be helpful. It would allow you to decompress and let go of that same busyness to the day. This seems like it would be a good way to clear out the energy and thoughts and worries of the day onto the page before drifting off to a restful and peaceful sleep.