Is occupational journaling a waste of time or a good idea?

My professor said PhD students who kept a journal log of their daily research activities sped up their graduation speed by over 1/3 so he made us write journals of our daily activities when we studied with him. I just think that my journal might take over 8 hours to write each week cause I do so many different things during my writing process.

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I'm not a PhD student and only did a partial semester of graduate training when we mutually decided I was not ready for graduate school and was not interested in it either.
Is occupational journaling a waste of time or a good idea?
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